aducrf101: Rearrange stack and heap to maximize available stack space

Stack now starts at the top of RAM, heap starts after BSS, and
they grow towards each other.

cpu/arm/aducrf101/Common/GCC/ADuCRF101.ld

@@ -91,10 +91,8 @@ SECTIONS
         } > ram AT > flash
 
         .bss : {
-                /* Stack is in BSS */
                 . = ALIGN(8);
                 __bss_start = .;
-                *(.bss.stack)
                 *(.bss)
                 *(.bss.*)
                 *(COMMON)
@@ -102,4 +100,9 @@ SECTIONS
                 __bss_end = .;
                 end = .;
         } > ram
+
+        /* Heap grows up from "end" (after bss), and stack grows down from
+           the end of RAM. */
+        . = ORIGIN(ram) + LENGTH(ram);
+        stack_end = .;
 }

cpu/arm/aducrf101/Common/GCC/crt0.S

@@ -32,19 +32,8 @@
  * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef __STACK_SIZE
-#define __STACK_SIZE 1024
-#endif
-
 .equ SCB_VTOR, 0xE000ED08
 
-/* Stack */
-        .section .bss.stack
-stack_start:
-        .space __STACK_SIZE, 0
-stack_end:
-        .global stack_end
-
 /* Vector table */
         .macro handler name
         .long \name\()