dt-bindings: thermal: Add AOP regulator cooling device bindings

Add bindings for AOP regulator cooling device driver. This driver will
be used to place voltage floor restriction for RPMh controlled rail.

Change-Id: I80367fdc3f073f768c0115c882e88ed57b657cef
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>