staging: bcm2835-audio: Add support for simultanous HDMI and Headphone audio

staging: bcm2835-audio: Add support for simultanous HDMI and Headphone audio

The firmware for the Raspberry PI already supports simultanous output
of audio through both the HDMI and the Headphone jack.  The current
implementation of ALSA doesn't expose this well to user mode since
the firmware audio is represented as a single card.

A newer approach is taken here and a virtual card is created for each
output(HDMI, Headphones, and Traditional ALSA).  The firmware has
the concept of channels or streams for which the number to use is
passed in the device tree. These streams are allocated to each of the
virtual cards.

As a side effect of this change, since each output is represented
independenly it's now very easy to use PulseAudio to control the
priorities of the outputs.

Testing:

Audacity and VLC were both loaded at the same time.  Each application
was assigned to a different card. With this change I was able to play
different music files at the same time through the HDMI and Headphones
jacks and control the audio independently.

Signed-off-by: Michael Zoran <mzoran@crowfest.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>