reduce stack size on Zero because of limited RAM

Author: stevew817

libraries/mbed/targets/cmsis/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32ZG_STK3200/TOOLCHAIN_ARM_MICRO/startup_efm32zg.s

@@ -29,7 +29,7 @@
 ;   <o> Stack Size (in Bytes) <0x0-0xFFFFFFFF:8>
 ; </h>
 
-Stack_Size      EQU     0x00000400
+Stack_Size      EQU     0x00000200
 
                 AREA    STACK, NOINIT, READWRITE, ALIGN=3
 Stack_Mem       SPACE   Stack_Size

libraries/mbed/targets/cmsis/TARGET_Silicon_Labs/TARGET_EFM32/TARGET_EFM32ZG_STK3200/TOOLCHAIN_GCC_ARM/startup_efm32zg.S

@@ -37,7 +37,7 @@
 #ifdef __STACK_SIZE
     .equ    Stack_Size, __STACK_SIZE
 #else
-    .equ    Stack_Size, 0x400
+    .equ    Stack_Size, 0x200
 #endif
     .globl    __StackTop
     .globl    __StackLimit