arm64: dts: imx8mn: remove otg1 power domain dependency on hsio

pgc_otg1 is an independent power domain of hsio, it's for usb phy,
so remove hsio power domain from its node.

Fixes: 8b8ebec6 ("arm64: dts: imx8mn: add GPC node")
Signed-off-by: Li Jun <jun.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>