ASoC: msm: Support multichannel playback over proxy port

Increase the period size in proxy driver to allow ten millisecond
worth data for capturing multichannel content.Add kcontrol to
allow configuring the proxy backend to six channels.

Change-Id: I1a3c7bf2cde686134f22d2a9a1737909cb2c3729
Signed-off-by: Krishnankutty Kolathappilly <kkolat@codeaurora.org>