drm/msm/dp: add dp phy 4.2.0 support

Some of the dp/dp phy register offsets changed
on dp phy 4.2.0 version. Patch adds dp phy version
support, maps register offsets based on phy version.

Change-Id: Ie2c0b364be937513f8f0b852f31da5eec9f8887b
Signed-off-by: Alexander Beykun <abeykun@codeaurora.org>