[mmal] Add MMAL decoder and MMAL renderer for Raspberry Pi

While omxplayer is the best performing player on the Pi (and the only option for raw Blu-Rays)
there are some reasons to use dvdplayer on a Pi:

DVDs with menus do not work well with omxplayer
support of software decode for SD codecs like divx3, msmpeg, sorenson spark etc
omxplayer doesn't support alsa, so can't be used with USB and I2S sound cards
dvdplayer may behave better with dodgy timestamps and packet loss, e.g. with live TV

So this PR adds hardware acceleration to dvdplayer using the MMAL api.

There is also a MMAL based video renderer. Compared to using GL, this:
saves the processing cost of YUV->RGB conversion
saves the memory cost of the RGB textures for video frames (1080p = 3MB for YUV and 8MB for RGB)
allows high quality (cubic) scaling