ARM: dts: msm: add proxy supply property to GPIO controlled regulator

The change adds proxy supply entries to the GPIO controlled regulator
display_panel_avdd. It is necessary to add the regulator to the proxy
consumer list along with the regulator-boot-on property as this is the
only way to ensure that the vote on the regulator stays on till the
display driver is probed.

Change-Id: I955834dcd0ee93646c5700f7d174931d1b0f5ba7