App: IAR fix for 8fa3a7b6

Commit 8fa3a7b6 uses "Image$$ARM_LIB_STACK_MSP$$ZI$$Base" instead of
using the REGION_DECLARE macros in region.h. This causes link issues
with IAR.

Signed-off-by: TTornblom <thomas.tornblom@iar.com>
Change-Id: I00fb896d2005eb9e64e5a6869e3d6e1d814d43a7