ARM: dts: msm: add proxy vote for mdss gdsc for 8996

Add proxy vote for mdss and vensu gdsc so that gdsc
will not be turned off after hand off so that
cont-splash can work for the dsi pll-1 active only
case.

Change-Id: Ifaddd2961eccbe4e66f452cb153a81152a5537f2
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>