firmware: MMAL: Pass dec_params in opaque buffers

Pass the contents of the decoder params in opaque buffers, particularly to relay interlace properties

firmware: gpioman: Reduce huge amount of log spam

firmware: hdmi: add gencmd to limit rate of change of hdmi clock adjustment

firmware: services: Avoid bad behaviour from calling init functions more than once
See: https://github.com/raspberrypi/userland/issues/205

firmware: Remove dts_whole_frames config option
firmware: dtsbits: Handle parsing (and discarding) extension packets
See: http://forum.osmc.tv/showthread.php?tid=15538&pid=109277