asoc: dai-q6: set dp audio stream index

Add mixer control to update ctl index and stream index
to set to display port audio AFE port. Use the index to
set AFE params for the same.

Change-Id: If83b5b0802bb82a0e01fb01c7175472d2b1bb94e
Signed-off-by: Karthikeyan Mani <kmani@codeaurora.org>