CHROMIUM: drm/rockchip: Call drm_gem_object_release() to destroy GEM base

CHROMIUM: drm/rockchip: Call drm_gem_object_release() to destroy GEM base

When converting the driver to use shmem-backed GEMs for IOMMU-enabled
systems, we forgot to add calls to drm_gem_object_release(), which gave
us a quite nice memory leak. This patch adds the missing calls.

Fixes: f11d5f0 ("FROMLIST: drm/rockchip: Do not use DMA mapping API if
attached to IOMMU domain")

BUG=chrome-os-partner:57158
TEST=while true; do backlight_dbus_tool --set --percent=0 && sleep 8 &&
 backlight_dbus_tool --set --percent=100 && sleep 3 ; done

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/385456
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Daniel Kurtz <djkurtz@chromium.org>
Conflicts:
	drivers/gpu/drm/rockchip/rockchip_drm_gem.c

Change-Id: I3c7b21ed22cfb38f512150f76fced3b0cc2b296d
Signed-off-by: Randy Li <randy.li@rock-chips.com>