drm: xilinx: dp: Initialize the phy when resuming

drm: xilinx: dp: Initialize the phy when resuming

The phy needs to be initialized / released accordingly when DP goes
into suspend / resume. Add functions for phy initializeiont / release,
and those functions can be shared with probe / remove sequence.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>