drm: zte: use devm_of_platform_populate()

Use devm_of_platform_populate() to be sure that of_platform_depopulate
is called when removing the driver.

Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
CC: Shawn Guo <shawnguo@kernel.org>
CC: David Airlie <airlied@linux.ie>
CC: dri-devel@lists.freedesktop.org
CC: linux-kernel@vger.kernel.org
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Link: http://patchwork.freedesktop.org/patch/msgid/1496072763-31209-4-git-send-email-benjamin.gaignard@linaro.org