drm/msm/shd: update base display mode at enable stage

Currently the base display mode for shared display is updated
at probe stage, which will be lost during lastclose. This change
will update base display mode at enable stage to fix the problem.

Change-Id: I0ce446d67da5cc4a57ae1c5c554e7e3798591acc
Signed-off-by: Xiaowen Wu <wxiaowen@codeaurora.org>