drm/i915/ltphy: Read PHY_VDR_0_CONFIG register

drm/i915/ltphy: Read PHY_VDR_0_CONFIG register

Read PHY_VDR_0_CONFIG to check if there is any change in the register and
decide based on that if P2P sequence to change the data rate of LT PHY
are required or not. This scenario only happens if the requested mode
uses 1.62Gbps with DP mode since LT PHY defaults to this mode if
any other mode is requested we need to follow the whole sequence.

Signed-off-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patch.msgid.link/20251101032513.4171255-8-suraj.kandpal@intel.com