drm: xilinx: crtc: Add crtc set config helper

drm: xilinx: crtc: Add crtc set config helper

The goal is to be able to synchronize resolution changes between the
drm device and emulated fbdev device if both devices are used by an
application e.g. in Qt we use both graphics and video layer whereas
the former is controlled by fbdev and the latter by drm. This patch
propagates resolution changes from the drm device to fbdev. Before
setting the new mode, a copy of the old mode is saved locally and
restored upon last close.

work in progres:
If hot-plug events happen while the application is running, the mode
pre-application start will be restored instead of the mode set by the
last hot-plug event. For example if we switch monitors from 1080p to
4k while the application is running, last close will restore the
fbconsole to 1080p on the 4k monitor.

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