soc: imx: gpcv2: keep i.MX8MN gpumix bus clock enabled

Like the i.MX8MM, keep the gpumix clocks running when the
domain is active.

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>