drm/sun4i: Add support for H6 HDMI PHY

H6 has Synopsys DWC HDMI 2.0 TX PHY.

There is no freely available documentation for it, only code found in
BSP kernel. However, judging by the code, PHY is very similar to older
Synopsys HDMI PHY described in i.MX6 documentation. Most registers seem
to be the same.

According to i.MX6 documentation, mpll settings are based on pixel clock
and are not specific to each SoC. Because of that, mpll table in this
commit is based on that documentation and not on BSP code. Other PHY
settings were derived from BSP PHY driver code.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181104182705.18047-23-jernej.skrabec@siol.net