drm/omap: fix uninit order in pdev_remove()

When unloading omapdrm driver, the omapdrm platform device is
uninitialized last, after the displays have been disconnected omap_crtc
callbacks have been removed. As the omapdrm pdev uninitialization needs
the features uninitialized in earlier steps, a crash is guaranteed.

This patch fixes the uninitialize order so that the omapdrm pdev is
removed first.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Rob Clark <robdclark@gmail.com>