[mythtv] V4L2_PIX_FMT_NV12M for amlogic hw decode support?

[Piotr Oniszczuk]

Mark,

Just small progress report regarding myth on some arm systems.

Fixing issue with playback black screen on arm mali gpu is progressing well :-)
I can now play some videos with yv12 renderer on mali. 

It looks however that amlogic hw decoder uses multiplanar nv12 pix fmt. (nv12m). 
By this I add V4L2_PIX_FMT_NV12M in checks at mythtv/libs/libmythtv/mythv4l2m2mcontext.cpp#L262
Unfortunately any attempt to play content with v4l2 m2m decode on s905 v4l2 gives error like in log: https://pastebin.com/FnYrNvn7

Let me know what You think!