phy: Add Amlogic AXG MIPI PCIe Analog PHY driver

The Amlogic AXG MIPI + PCIe Analog PHY provides function for both PCIe and
MIPI DSI at the same time, and provides the Analog part of MIPI DSI transmission
and Analog part of the PCIe lines.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>