samsung/exynos*/Makefile.inc: Simplify unnecessary ifeq

It's not needed, as we can use a simpler macro instead.

Change-Id: Ib96f5cfa434d0383ee3bfe49995a8f8830987f20
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/7925
Reviewed-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Tested-by: build bot (Jenkins)