soc: imx: gpcv2: allow domains without power-sequence control

Some of the PGC domains only control the handshake with the ADB400
and don't have any power sequence controls. Make such domains work
by allowing the pxx and map bits to be empty and skip all actions
using those controls.

Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>