Some camera modules have the SoC feeding a master clock to the sensor
instead of having a standalone crystal. This clock signal is generated
from the clock control unit and output from the CSI MCLK function of
pin PE1.

Add a pinmux setting for it for camera sensors to reference.
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>