phy: amlogic: Add AXG MIPI D-PHY driver

The Amlogic AXG SoCs embeds a MIPI D-PHY used to communicate with DSI
panels.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Link: https://lore.kernel.org/r/20201116101315.71720-3-narmstrong@baylibre.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>