ARM: dts: msm: add proxy consumers for display regulators for msm8994

PM8994 regulators L2, L12, L14 and L28 are enabled in
the boot loader 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: I7b040b84da5ce5bdf80633ac5461be327909b902
Signed-off-by: Dhaval Patel <pdhaval@codeaurora.org>