Add app_start config system support for NRF52840 for bootloader

targets/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52840/device/TOOLCHAIN_ARM_STD/nRF52832.sct

@@ -1,13 +0,0 @@
-LR_IROM1 0x21000 0x00DF000  {
-  ER_IROM1 0x21000 0x00DF000  {
-   *.o (RESET, +First)
-   *(InRoot$$Sections)
-   .ANY (+RO)
-  }
-  RW_IRAM0 0x20003288 UNINIT 0x000000F8  { ;no init section
-        *(*noinit)
-  }
-  RW_IRAM1 0x20003380 0x0003cc80  {
-   .ANY (+RW +ZI)
-  }
-}

targets/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52840/device/TOOLCHAIN_ARM_STD/nRF52840.sct

@@ -0,0 +1,23 @@
+#! armcc -E
+
+#if !defined(MBED_APP_START)
+  #define MBED_APP_START 0x21000
+#endif
+
+#if !defined(MBED_APP_SIZE)
+  #define MBED_APP_SIZE 0xDF000
+#endif
+
+LR_IROM1 MBED_APP_START MBED_APP_SIZE  {
+  ER_IROM1 MBED_APP_START MBED_APP_SIZE  {
+   *.o (RESET, +First)
+   *(InRoot$$Sections)
+   .ANY (+RO)
+  }
+  RW_IRAM0 0x20003288 UNINIT 0x000000F8  { ;no init section
+        *(*noinit)
+  }
+  RW_IRAM1 0x20003380 0x0003cc80  {
+   .ANY (+RW +ZI)
+  }
+}

targets/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52840/device/TOOLCHAIN_GCC_ARM/NRF52840.ld

@@ -16,9 +16,17 @@
 
 /* Linker script to configure memory regions. */
 
+#if !defined(MBED_APP_START)
+    #define MBED_APP_START 0x21000
+#endif
+
+#if !defined(MBED_APP_SIZE)
+  #define MBED_APP_SIZE 0xDF000
+#endif
+
 MEMORY
 {
-  FLASH (rx) : ORIGIN = 0x21000, LENGTH = 0xDF000
+  FLASH (rx) : ORIGIN = MBED_APP_START, LENGTH = MBED_APP_SIZE
   RAM (rwx) :  ORIGIN = 0x20003288, LENGTH = 0x3cd78
 }
 
@@ -130,7 +138,7 @@ SECTIONS
         PROVIDE(__start_fs_data = .);
         KEEP(*(.fs_data))
         PROVIDE(__stop_fs_data = .);
-        
+
         *(.jcr)
         . = ALIGN(4);
         /* All data end */
@@ -146,7 +154,7 @@ SECTIONS
       KEEP(*(.noinit))
       PROVIDE(__stop_noinit = .);
     } > RAM
-    
+
     .bss :
     {
         . = ALIGN(4);

targets/TARGET_NORDIC/TARGET_NRF5/TARGET_MCU_NRF52840/device/TOOLCHAIN_IAR/nRF52840.icf

@@ -1,15 +1,26 @@
 /*###ICF### Section handled by ICF editor, don't touch! ****/
 /*-Editor annotation file-*/
 /* IcfEditorFile="$TOOLKIT_DIR$\config\ide\IcfEditor\cortex_v1_0.xml" */
+
+if (!isdefinedsymbol(MBED_APP_START)) {
+    define symbol MBED_APP_START = 0x21000;
+}
+
+if (!isdefinedsymbol(MBED_APP_SIZE)) {
+    define symbol MBED_APP_SIZE = 0xDF000;
+}
+
 /*-Specials-*/
-define symbol __ICFEDIT_intvec_start__ = 0x21000;
+define symbol __ICFEDIT_intvec_start__ = MBED_APP_START;
+
 /*-Memory Regions-*/
-define symbol __ICFEDIT_region_ROM_start__   = 0x21000;
+define symbol __ICFEDIT_region_ROM_start__   = MBED_APP_START;
-define symbol __ICFEDIT_region_ROM_end__     = 0xfffff;
+define symbol __ICFEDIT_region_ROM_end__     = MBED_APP_START + MBED_APP_SIZE - 1;
 define symbol __ICFEDIT_region_RAM_start__   = 0x20003288;
 define symbol __ICFEDIT_region_RAM_end__     = 0x2003ffff;
 export symbol __ICFEDIT_region_RAM_start__;
 export symbol __ICFEDIT_region_RAM_end__;
+
 /*-Sizes-*/
 /*Heap 1/4 of ram and stack 1/8*/
 define symbol __ICFEDIT_size_cstack__   = 0x800;

targets/targets.json

@@ -3239,7 +3239,8 @@
         "macros_add": ["BOARD_PCA10056", "CONFIG_GPIO_AS_PINRESET", "SWI_DISABLE0", "NRF52_ERRATA_20"],
         "device_has_add": ["FLASH", "ANALOGIN", "I2C", "I2C_ASYNCH", "INTERRUPTIN", "LOWPOWERTIMER", "PORTIN", "PORTINOUT", "PORTOUT", "PWMOUT", "RTC", "SERIAL", "SERIAL_ASYNCH", "SERIAL_FC", "SLEEP", "SPI", "SPISLAVE", "TRNG"],
         "release_versions": ["2", "5"],
-        "device_name": "nRF52840_xxAA"
+        "device_name": "nRF52840_xxAA",
+        "bootloader_supported": true
     },
     "BLUEPILL_F103C8": {
         "inherits": ["FAMILY_STM32"],