drm/msm/sde: sde encoder store the current mode info

This change queries the latest mode info from the connector
and stores this information in the encoder data structure. This
prevents repeated querying and copying of the info at the time of
use.

Change-Id: I0639f4800fcceda135dfbafb759f8fb59152df55
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>
Signed-off-by: Samantha Tran <samtran@codeaurora.org>