GKI: drm: samsung: populate gem object functions before init

Upstream change d693def4fd1c2 ("drm: Remove obsolete GEM and PRIME
callbacks from struct drm_driver") requires obj->base.funcs to be
populated before calling drm_gem_private_object_init(). This patch
assigns required definitions from exynos_drm_gem_object_funcs.

Signed-off-by: Carlos Llamas <cmllamas@google.com>
Change-Id: I1505926258db4fe07916e22b92fdd4229736e170