msm: mdss: program HDMI/DP core select during interface setup

Program the HDMI/DP core select register during interface setup
since this acts as a mux select for shared interface with LPASS
for audio programming. The mux value is set to 1 for DP and to
0 for HDMI and all other panels.

CRs-Fixed: 1009284
Change-Id: I3283c6255f9cdbbfbffc47057c60b30eb7bdacde
Signed-off-by: Tatenda Chipeperekwa <tatendac@codeaurora.org>