Alsa support for Maemo SDK (n770): External PCM IO plugin

Alsa support for Maemo SDK (n770): External PCM IO plugin

This patch file adds an ALSA External PCM I/O plugin. This source uses
the dsp-protocol
implementation.

The plugin probes for a free communication channel at the start time.
It will probe only
for channels specified into the configuration file for the plugin. An
configuration example is:
# PCM
       pcm.!default {
               type alsa_dsp
               playback_device_file ["/dev/dsptask/pcm2"]
               recording_device_file ["/dev/dsptask/pcm_rec"]
       }

The plugin supports the following:

    *  Playback:
          o 16-bit PCM formats:
                + S16_LE
                + S16_BE
                + U16_LE
                + U16_BE
          o 8-bit PCM formats:
                + A_LAW
                + MU_LAW
                + U8
                + S8
          o Rates:
                + 8 KHz
                + 11.025 KHz
                + 12 KHz
                + 16 KHz
                + 22.050 KHz
                + 24 KHz
                + 32 KHz
                + 44.1 KHz
                + 48 KHz
          o Channels:
                + Mono
                + Stereo
    * Recording:
          o 16-bit PCM formats:
                + S16_LE
          o 8-bit PCM formats:
                + A_LAW
                + MU_LAW
          o Rates:
                + 8 KHz
          o Channels
                + Mono

Signed-off-by: Eduardo Valentin <eduardo.valentin@indt.org.br>