pipewiresink: set a default channel map if the number of channels is fixed

pipewiresink: set a default channel map if the number of channels is fixed

-This allows remaping streams using pipewiresink to match the channel layout
of the target device

Bug-AGL: SPEC-4241
Change-Id: I4090187dc9977fc3d0ee440b601cb95f6864a9cf
Signed-off-by: Ashok Sidipotu <ashok.sidipotu@collabora.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/27130
Reviewed-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jenkins Job builder account
ci-image-build: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account