[EFM32] Use targets.json to improve directory structure

Now that we have targets.json, we get target inheritance and can use it to clean up the EFM32 folder structure.
* In the top-level EFM32 folder, there are now folders per MCU family (Giant, Leopard, ...)
* Those family folders contain the CMSIS headers in the 'device' subfolder, as well as global family headers (i.e. mapping of pins to peripherals)
* Inside of the family folder, there is a per-target folder containing target settings. In the future, we'll want to get rid of those by using the config system provided by targets.json

targets/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32GG/PeripheralNames.h

@@ -60,10 +60,6 @@ typedef enum {
     LEUART_1 = LEUART1_BASE
 } UARTName;
 
-#define STDIO_UART_TX     USBTX
-#define STDIO_UART_RX     USBRX
-#define STDIO_UART        UART0
-
 typedef enum {
     SPI_0 = USART0_BASE,
     SPI_1 = USART1_BASE,

targets/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32GG/TARGET_EFM32GG_STK3700/PinNames.h

@@ -50,7 +50,11 @@ typedef enum {
     SERIAL_RX   = PD1,
     USBTX       = PE0,
     USBRX       = PE1,
-    EFM_BC_EN   = PF7
+
+    /* Board Controller */
+    STDIO_UART_TX = USBTX,
+    STDIO_UART_RX = USBRX,
+    EFM_BC_EN     = PF7
 } PinName;
 
 #ifdef __cplusplus

targets/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32GG/TARGET_EFM32GG_STK3700/device_peripherals.h

@@ -36,6 +36,9 @@
 /* USB */
 #define USB_TIMER USB_TIMER1
 
+/* STDIO */
+#define STDIO_UART UART0
+
 /* Clocks */
 
 /* Clock definitions */

targets/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32HG/TARGET_EFM32HG_STK3400/PinNames.h

@@ -50,7 +50,11 @@ typedef enum {
     SERIAL_RX   = PE11,
     USBTX       = PF2,
     USBRX       = PA0,
-    EFM_BC_EN   = PA9
+
+    /* Board Controller */
+    STDIO_UART_TX = USBTX,
+    STDIO_UART_RX = USBRX,
+    EFM_BC_EN     = PA9
 } PinName;
 
 #ifdef __cplusplus

targets/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32HG/TARGET_EFM32HG_STK3400/device_peripherals.h

@@ -36,6 +36,9 @@
 /* USB */
 #define USB_TIMER USB_TIMER2
 
+/* STDIO */
+#define STDIO_UART USART1
+
 /* Clocks */
 
 /* Clock definitions */