phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI CSI-2

phy: allwinner: phy-sun6i-mipi-dphy: Support D-PHY Rx mode for MIPI CSI-2

The Allwinner A31 D-PHY supports both Rx and Tx modes. While the latter
is already supported and used for MIPI DSI this adds support for the
former, to be used with MIPI CSI-2.

This implementation is inspired by Allwinner's V3s Linux SDK
implementation, which was used as a documentation base.

It uses the direction dt property to distinguish between tx and rx
directions.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
Link: https://lore.kernel.org/r/20220415152138.635525-3-paul.kocialkowski@bootlin.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>