regulator: kryo-regulator: switch regulators to BHS prior to M4M collapse

Due to unexpected interactions with the M3 low power mode, the
clusters must be powered through the BHS before entering the M3 state.
To satisfy this requirement, subscribe to CPU PM notifications and ensure
that the regulators are placed in bypass (BHS) mode when entering such
state. On the resume path, restore the configuration existing prior to
entering M3 in order to guarantee that the consumers' internal state and
the true kryo regulator states are kept in sync.

Change-Id: I65fbbd06e9a8af272fa2f976bfe161b5ec383ce1
Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>