drm/msm/shd: populate panel width and height for shared virtual display

Populate the actual panel width and height from base connector to shared
virtual connector during connector detect callback.

Change-Id: Icc6b5ba96c88d07794af826bff0357fe171b0310
Acked-by: Krishna Kishor Jha <kkishoj@qti.qualcomm.com>
Signed-off-by: Rahul Sharma <rahsha@codeaurora.org>