ASoC: msm8x10: add support to split SD0/1 as two seperate BE

SD0 and SD1 are driven by single DMA channel. this makes it
impossible for any audio session to be sent to SD1 output
without mixing with SD0 data contents.

Allow user to route audio to a new AFE PORT introduced to
send data to SD1 without mixing with SD0 contents. The user
however needs to group the ports before opening any of the
AFE ports.

Change-Id: Icadc0f87fffc29575f069b6124dee3cf9d8a9fcd
Signed-off-by: Asish Bhattacharya <asishb@codeaurora.org>