soc: imx: gpcv2: keep i.MX8M* bus clocks enabled

Annotate the domains with bus clocks to keep those clocks enabled
as long as the domain is active.

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