MLK-16581-7 drm/imx: ldb: Add system power management support

This patch adds system power management support for imx-ldb drm driver
by proper PHY power/exit/init handling where necessary and pixel link
re-initialization in the resume operation.  The driver depends on the
imx-drm core driver to handle ldb bridge power management operations.

Signed-off-by: Liu Ying <victor.liu@nxp.com>