regulator: Call proxy-consumer functions for each regulator registered

Add a call to regulator_proxy_consumer_register() at the end of
regulator_register() and a call to
regulator_proxy_consumer_unregister() at the beginning of
regulator_unregister().  These calls ensure that proxy consumer
features may be used by any type of regulator regardless of the
driver supporting it.

Change-Id: Ia70da1df47042fa673c42f389136557f868d19a3
Signed-off-by: David Collins <collinsd@codeaurora.org>