ARM: dts: msm: Add proxy consumer properties for regulators on msm8992

PM8994 regulators L2, L12, L14 and L28 are enabled in the bootloader
when it is configured to use the continuous splash screen feature.
If any of these regulators are disabled before the high level OS
display driver initializes, then the display will fade out.

Add proxy-consumer properties for these regulators so that they are
kept enabled in high power mode until all consumers have been able
to make their requests.

Change-Id: Id8d70848149ba39be2f12683fea1c24f56538a2c
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>