ASoC: msm: q6dspv2: add SLIMBUS6 RX routings for Slimbus 7/8

Slimbus TX 7 and 8 would need to be connected to Slimbus RX 6
for different use cases using loopback in AFE. Updated necessary
routings for supporting the loopback.

CRs-Fixed: 1036018
Change-Id: I46c797a6550884bf42a2d7763590047d2e750906
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>