MCU_NRF52832: use two-region memory layout (stack + heap) to support MicroLib

MicroLib is the lightweight C lib for the Arm toolchain and
used as the default C lib on bare metal builds with the Arm
toolchain. It requires two separate memory regions for stack
and heap.

The change is based on nRF52840.sct.

Author: LDong-Arm

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52832/device/TOOLCHAIN_ARM_STD/nRF52832.sct

@@ -26,22 +26,24 @@
 
 #define MBED_RAM0_START MBED_RAM_START
 #define MBED_RAM0_SIZE  0xE0
-#define MBED_RAM1_START (MBED_RAM_START + MBED_RAM0_SIZE)
+#define MBED_RAM1_START (MBED_RAM0_START + MBED_RAM0_SIZE)
 #define MBED_RAM1_SIZE  (MBED_RAM_SIZE - MBED_RAM0_SIZE)
+#define RAM_FIXED_SIZE  (MBED_CONF_TARGET_BOOT_STACK_SIZE + MBED_RAM0_SIZE)
 
 LR_IROM1 MBED_APP_START MBED_APP_SIZE {
   ER_IROM1 MBED_APP_START MBED_APP_SIZE {
    *.o (RESET, +First)
-   *(InRoot$$Sections) 
+   *(InRoot$$Sections)
    .ANY (+RO)
   }
-
   RW_IRAM0 MBED_RAM0_START UNINIT MBED_RAM0_SIZE { ;no init section
         *(*nvictable)
   }
   RW_IRAM1 MBED_RAM1_START MBED_RAM1_SIZE {
    .ANY (+RW +ZI)
   }
-  ARM_LIB_STACK MBED_RAM1_START+MBED_RAM1_SIZE EMPTY -Stack_Size { ; Stack region growing down
+  ARM_LIB_HEAP AlignExpr(+0, 16) EMPTY (MBED_RAM_SIZE - RAM_FIXED_SIZE + MBED_RAM_START - AlignExpr(ImageLimit(RW_IRAM1), 16)) {
+  }
+  ARM_LIB_STACK MBED_RAM1_START + MBED_RAM1_SIZE EMPTY - Stack_Size { ; Stack region growing down
   }
 }