soc: imx: gpcv2: move domain mapping to domain driver probe

As long as the power domain driver is active we want power control
over the domain (which is what the mapping bit requests), so there
is no point in whacking it for every power control action, simply
set the bit in driver probe and clear it when the driver is removed.

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>