HDMI support

[alyssarosenzweig]

In theory, @anholt's tree should support graphics out-of-the-box, although things are rarely that simple.

[christinaa]

We need to bring up HDMI power as well as set up some clocks (PLLH especially which is a bit weird). We also need to provide power management interfaces in the 2nd stage firmware.

[anholt]

For HDMI in Linux, there's now HDMI power domain support in https://lkml.org/lkml/2018/11/20/1320.

I haven't tested it. This power domain doesn't do the HDMI swing settings, which I suspect should be in a PHY or something instead. However, this project probably wants to know about that driver for USB support. :)