mei: me: change power gating function name conventions

The current power gating naming was confusing,
we wish to swap meanings of register and flow level power gating terms,

For registers writing level use terms set and unset:
	mei_me_pg_set, mei_me_pg_unset

For flow/high level use power gating enter and power gating exit terms
	mei_me_pg_enter_sync, mei_me_pg_exit_sync

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>