drivers: mipi_dsi: dsi_mcux: make DPI mode optional

Only setup DPI input from LCDIF if MODE_VIDEO is set, as this
is the the only case where input from the LCDIF would be required to
drive the display. Do not populate the dpi_config structure unless a
reference the the NXP LCDIF device is provided, since this is the output
device providing DPI data.

Signed-off-by: Daniel DeGrasse <daniel.degrasse@nxp.com>