Add heaplimit to NRF52 devices

Author: deepikabhavnani

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52832/device/TOOLCHAIN_GCC_ARM/NRF52832.ld

@@ -238,6 +238,7 @@ SECTIONS
         /* Expand the heap to reach the stack boundary. */
         ASSERT(. <= (ORIGIN(RAM) + LENGTH(RAM) - MBED_BOOT_STACK_SIZE), "heap region overflowed into stack");
         . = ORIGIN(RAM) + LENGTH(RAM) - MBED_BOOT_STACK_SIZE;
+        __HeapLimit = .;
     } > RAM
     PROVIDE(__heap_start = ADDR(.heap));
     PROVIDE(__heap_size = SIZEOF(.heap));

targets/TARGET_NORDIC/TARGET_NRF5x/TARGET_NRF52/TARGET_MCU_NRF52840/device/TOOLCHAIN_GCC_ARM/NRF52840.ld

@@ -254,6 +254,7 @@ SECTIONS
         /* Expand the heap to reach the stack boundary. */
         ASSERT(. <= (ORIGIN(RAM) + LENGTH(RAM) - MBED_BOOT_STACK_SIZE), "heap region overflowed into stack");
         . = ORIGIN(RAM) + LENGTH(RAM) - MBED_BOOT_STACK_SIZE;
+        __HeapLimit = .;
     } > RAM
     PROVIDE(__heap_start = ADDR(.heap));
     PROVIDE(__heap_size = SIZEOF(.heap));