drm/exynos: remove function check_gem_flags

The function check_gem_flags is too simple, so it's better to move codes
in each consumer functions.

Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>

diff --cc drivers/gpu/drm/exynos/exynos_drm_gem.c
Simple merge