asoc: qcs405: Add AFE Tx loopback controls

AFE Tx loopback is used to capture playback data from Rx port
and use it for echo reference. Add controls to configure
capture backend channels, sample rate and format.

Change-Id: I68bd89461f3f37870a6d946fb03fe4124ee2fa6f
Signed-off-by: Chaithanya Krishna Bacharaju <chaithan@codeaurora.org>