ASoC: routing: update echo reference index for dp

Add display port 1 to the end of echo reference rx array. This avoids
shifting the existing ports and their index mapping.
Add a new switch case to return the echo reference port id for
display port 1.

CRs-Fixed: 2511612
Change-Id: I2ba9cf5e9c9fc687d429a04f40a32231c0913f5e
Signed-off-by: Vignesh Kulothungan <vigneshk@codeaurora.org>