dt-bindings: Add power-on.h for PMIC PON definitions

This snapshot is taken as of msm-4.4 commit 4594178f22e3
("Merge "leds: qpnp-flash-v2: Fix pinctrl configuration"").

Change-Id: I456d115a42b35cce91fcef18e6e69124e3f195e2
Signed-off-by: Subbaraman Narayanamurthy <subbaram@codeaurora.org>