drivers: mipi_dsi: make DPI mode optional for dsi_mcux_2l driver

Make DPI mode an optional configuration for the DSI MCUX 2L driver.
DPI mode will only be enabled when the MIPI is attached in video mode,
since this is when DPI formatted packets are expected.

This will enable the DSI driver to also support DBI/command mode, for
displays that use this format.

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