cortex-m: Fix flash size calculation boards without flash
cortex-m: Fix flash size calculation boards without flash

CL:2334389 broke the make debug output for the kukui_scp and
flapjack_scp boards. The actual EC image was not affected.

This change also cleans up the #ifdef usage to consolidate assignment of
the output sections into one place.

BUG=b:164696005
BRANCH=none
TEST=make buildall
TEST=Run "util/compare_board.sh -b cortex-m"

Signed-off-by: Keith Short <f6d578f97033c25f1206cb57d52f358974c82954@chromium.org>
Change-Id: If69cb492e2aa5f1181e27be24ee66f63cc74ff62
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/2359492
Reviewed-by: caveh jalali <08e24a66aefda7a55ca7d73f8903e0fb16eec763@chromium.org>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec