arm64: dts: imx8mm-venice-gw7901.dts: disable pgc_gpumix

Since commit b21269b12e48 ("arm64: dts: imx8mm: add GPC node") the
GW7901 will hang during kernel init because it does not power the unused
GPU voltage rails on the IMX8MM. Disable pgc_gpumix to work around this.

We also disable the GPU devices that depend on the gpumix power domain
and pgc_gpu to avoid them staying in a probe deferred state forever.

Additionally as the MIPI voltage rail is also not connected on this
board we disable pgc_mipi and disp_blk_ctrl.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>