drm/vc4: Don set gem_obj->resv in prime import anymore

This is done in drm_prime.c now.

Reviewed-by: Eric Anholt <eric@anholt.net>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190614203615.12639-48-daniel.vetter@ffwll.ch