exynos: Apply format usage flag hack to YUV420P

This is needed for planar format video in
addition to semiplanar.  Also, update the flag
to be more representative of what it REALLY does,
which is merely to add GRALLOC_USAGE_HW_FIMC1.

This fixes Netflix on Note 10.1 so it no
longer needs Developer Options hacks.

Change-Id: I31df87c252779e66a056b79b1f48779024ec0f30