asoc: add code change for proxy playback and capture BE DAIs.

proxy AFE port based BE DAIs can be used for various use cases, including
but not limited to voice call. Add support for BE DAI link based on pseudo
ports.

Change-Id: Ifb6d9c894dcaf6080040d9bcd6f364ceda17e60a
Signed-off-by: Sujin Panicker <spanic@codeaurora.org>