regulator: cpr3-regulator: add debugfs closed-loop mode selection support

Add support to switch between closed-loop (CPR controller loop
enabled) and open-loop (CPR controller loop disabled) operating
modes for each CPR controller using debugfs.  Also add support to
switch between software closed-loop and hardware closed-loop
modes on CPR controllers that support it.

Change-Id: I786166fb703e701e9eb0d595fdec451e86e8949d
Signed-off-by: David Collins <collinsd@codeaurora.org>