ENGR00275419-1 mxc dispdrv: introduce post init interface

ENGR00275419-1 mxc dispdrv: introduce post init interface

This patch adds a new post init interface in the mxc display
driver. It may do necessary deferred operations after a
display device's dev_id and disp_id pass usage check. This
is a feasible way to avoid any setup being overwitten or
damaged by a late coming display device which uses the same
dev_id and disp_id with a display already registered.

Signed-off-by: Liu Ying <Ying.Liu@freescale.com>