mei: hbm: reorganize the power gating responses

Before adding support for D0i3 we need to reorganize the hbm pg handling
Move HBM PG response code to dedicated functions in order to unclutter
hbm command switch.
Add check for the right system state before message processing and
return -EPROTO in state mismatch case.

Signed-off-by: Alexander Usyskin <alexander.usyskin@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>