Update linker files and resolve build issue

Linker files for LPC11U68 and LPC1549 updated as Mbed OS memory model
1.	LPC1549
Has multiple memory banks, 4K bank used for stack exclusively and 16K for Heap
Its is mbed 2 only target hence 4K for stack.

2.	LPC11U68
Added Heap and Stack sections in linker files. Resolved build issues.

targets/TARGET_NXP/TARGET_LPC11U6X/device/TOOLCHAIN_GCC_ARM/TARGET_LPC11U68/LPC11U68.ld

@@ -8,6 +8,13 @@
  * By LPCXpresso v7.2.0 [Build 153] [2014-05-19]  on Sat Jun 14 15:26:54 JST 2014
  */
 
+ 
+#if !defined(MBED_BOOT_STACK_SIZE)
+    #define MBED_BOOT_STACK_SIZE 0x400
+#endif
+
+STACK_SIZE = MBED_BOOT_STACK_SIZE;
+
 MEMORY
 {
   /* Define each memory region */
@@ -229,7 +236,32 @@ SECTIONS
          . = ALIGN(8) ;
         _end_noinit = .;
     } > Ram0_32
-    
+
     PROVIDE(_pvHeapStart = .);
-    PROVIDE(_vStackTop = __top_Ram0_32 - 0);
+    .heap :
+    {
+        __end__ = .;
+        end = __end__;
+        *(.heap*)
+        . = ORIGIN(Ram0_32) + LENGTH(Ram0_32) - STACK_SIZE;
+        __HeapLimit = .;
+    } > Ram0_32
+
+
+    /* .stack_dummy section doesn't contains any symbols. It is only
+     * used for linker to calculate size of stack sections, and assign
+     * values to stack symbols later */
+    .stack_dummy :
+    {
+        *(.stack)
+    } > Ram0_32
+
+    /* Set stack top to end of RAM, and stack limit move down by
+     * size of stack_dummy section */
+    __StackTop = ORIGIN(Ram0_32) + LENGTH(Ram0_32);
+    __StackLimit = __StackTop - STACK_SIZE;
+    PROVIDE(__stack = __StackTop);
+    
+    PROVIDE(__stack = __StackTop);
+    PROVIDE(_vStackTop = __StackTop);
 }

targets/TARGET_NXP/TARGET_LPC15XX/device/TOOLCHAIN_GCC_ARM/LPC1549.ld

@@ -138,8 +138,10 @@ SECTIONS
         __end__ = .;
         end = __end__;
         *(.heap*)
+        . = ORIGIN(Ram1_16) + LENGTH(Ram1_16);
         __HeapLimit = .;
-    } > Ram0_16
+    } > Ram1_16
+
 
     /* .stack_dummy section doesn't contains any symbols. It is only
      * used for linker to calculate size of stack sections, and assign
@@ -147,11 +149,11 @@ SECTIONS
     .stack_dummy :
     {
         *(.stack)
-    } > Ram0_16
+    } > Ram2_4
 
     /* Set stack top to end of RAM, and stack limit move down by
      * size of stack_dummy section */
-    __StackTop = ORIGIN(Ram0_16) + LENGTH(Ram0_16) + LENGTH(Ram1_16) + LENGTH(Ram2_4);
+    __StackTop = ORIGIN(Ram2_4) + LENGTH(Ram2_4);
     __StackLimit = __StackTop - STACK_SIZE;
     PROVIDE(__stack = __StackTop);
     

targets/targets.json

@@ -511,6 +511,9 @@
             "SLEEP",
             "SPI"
         ],
+        "macros": [
+            "MBED_FAULT_HANDLER_DISABLED"
+        ],
         "default_lib": "small",
         "release_versions": ["2"],
         "device_name": "LPC11U68JBD100"