ARM: dts: msm: add proxy vote for DSI supplies for sm8150

For continuous splash screen feature, the display needs
to be kept alive during the kernel boot up. Add proxy
vote for all the regulator supplies needed to keep
the display alive.

Change-Id: Ia6229bffcd185ab2b6f9f9bdd6c42080187d5ccb
Signed-off-by: Ingrid Gallardo <ingridg@codeaurora.org>