dt-bindings: arm: fsl: add Skov Rev.C HDMI support

dt-bindings: arm: fsl: add Skov Rev.C HDMI support

From software perspective, Rev.C HDMI and Rev.B HDMI don't differ since
the panel is connected via HDMI and the touchscreen is connected via
USB. However, the bootloader firmware expects to find a dts with the
correct revc-hdmi compatible.

Signed-off-by: Marco Felsch <m.felsch@pengutronix.de>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>