drivers: mipi: delay initialization after display drivers

Currently MIPI devices are set to initialize before display drivers,
which is incoherent with how the mcux mipi-dsi device is declared in the
device tree.

This is detected with build time priority checking:

west build -p -b mimxrt595_evk_cm33 samples/drivers/display \
	     -DCONFIG_CHECK_INIT_PRIORITIES=y

ERROR: /soc/peripheral@50000000/mipi_dsi@31000 POST_KERNEL 40 <
		/soc/peripheral@50000000/lcdif@210000 POST_KERNEL 85

Note that this also changes the priority of dsi_stm32, though that
should be ok since does not appear to have other dependencies in
devicetree.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>