arm64: dts: imx8mm-venice-gw7904: disable disp_blk_ctrl

[ Upstream commit f7a0b575 ]

The GW7904 does not connect the VDD_MIPI power rails thus MIPI is
disabled. However we must also disable disp_blk_ctrl as it uses the
pgc_mipi power domain and without it being disabled imx8m-blk-ctrl will
fail to probe:
imx8m-blk-ctrl 32e28000.blk-ctrl: error -ETIMEDOUT: failed to attach
power domain "mipi-dsi"
imx8m-blk-ctrl: probe of 32e28000.blk-ctrl failed with error -110

Fixes: b999bdaf

 ("arm64: dts: imx: Add i.mx8mm Gateworks gw7904 dts support")
Signed-off-by: Tim Harvey <tharvey@gateworks.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>