[media] exynos-gsc: Add missing Makefile

Add missing Makefile that got lost while rebasing commit 655ceff1
"[media] gscaler: Add Makefile for G-Scaler Driver" onto latest source tree.

Signed-off-by: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>