Heap size reduced to 64k for IAR

IAR heap sizes were hard configured to be 96k which is 75% of the
total RAM available. Reduced it to be 64k which is half of the available RAM.

Author: Hasnain Virk

targets/TARGET_STM/TARGET_STM32F4/TARGET_MTS_DRAGONFLY_F411RE/device/TOOLCHAIN_IAR/stm32f411xe.icf

@@ -16,9 +16,9 @@ define region RAM_region = mem:[from __region_RAM_start__ to __region_RAM_end__]
 
 /* Stack and Heap */
 /* Stack: 4kB - 408B for vector table */
-/* Heap: 96kB */
+/* Heap: 64kB */
 define symbol __size_cstack__ = 0xe68;
-define symbol __size_heap__   = 0x18000;
+define symbol __size_heap__   = 0x10000;
 define block CSTACK    with alignment = 8, size = __size_cstack__   { };
 define block HEAP      with alignment = 8, size = __size_heap__     { };
 define block STACKHEAP with fixed order { block HEAP, block CSTACK };