soc: imx: imx8mp-blk-ctrl: Use dev_pm_domain_attach_by_name

The genpd_dev_pm_attach_by_name() is not exported, following error
occurs when building imx8mp-blk-ctrl as a module:

ERROR: modpost: "genpd_dev_pm_attach_by_name" [drivers/soc/imx/imx8mp-blk-ctrl.ko] undefined!

Fix this by using dev_pm_domain_attach_by_name() instead.

Signed-off-by: Jindong Yue <jindong.yue@nxp.com>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>