sw/vec: Increase heap size to 1.25M

Latest IREE change caused heap for mobilenet_v1 to increase over 1M and
cause a panic. Increase heap size to account for this.

Bug: 258243964
Fix: 258243964
Change-Id: I41a2f66ecf62b6942a9f12bf0ee81eda068ab572

springbok/springbok.ld

diff --git a/springbok/springbok.ld b/springbok/springbok.ld
index 7a80efb..ab6e3a7 100644
--- a/springbok/springbok.ld
+++ b/springbok/springbok.ld
@@ -27,7 +27,7 @@
         TEMPORARY_DATA (rw) : ORIGIN = 0x80000000 + 5*WINDOW_LENGTH, LENGTH = TCM_LENGTH
 }
 
-HEAP_SIZE = DEFINED(HEADP_SIZE) ? HEAP_SIZE : DEFINED(__heap_size__) ? __heap_size__ : 1M;
+HEAP_SIZE = DEFINED(HEADP_SIZE) ? HEAP_SIZE : DEFINED(__heap_size__) ? __heap_size__ : 1250K;
 STACK_SIZE = DEFINED(STACK_SIZE) ? STACK_SIZE : DEFINED(__stack_size__) ? __stack_size__ : 0x2000;
 
 ENTRY(_start)