dt-bindings: power: hl6111r: Add bindings

HL6111R is a wireless charging power receiver IC that has a maximum
power output of 15 W, a maximum current output of 2.2 A, and a
programmable output voltage range of 4 V to 20 V with different step
sizes. It supports both the A4WP and WPC wireless charging standards.

Change-Id: Idb276226c4855c83427913a5368deb70e3f2b04f