drm/sun4i: add support for R40 HDMI PHY

The R40 SoC has a HDMI PHY that is possible to mux two video PLLs.

Add support for it.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180916043409.62374-4-icenowy@aosc.io