regulator: cprh-kbss-regulator: add support for AVG initialization

Some CPRh controllers support the AVG feature. Add support to
initialize the CPR controller hardware register necessary to
enable this feature.

Change-Id: I5047b73f3f1528b9f828328b842e56a94acb2810
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>