Add dummy sound module for special test cases

Add dummy sound module for special test cases

Enable the dummy sound device as module so we can
load it on demand.

Bug-AGL: SPEC-3612
Signed-off-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Change-Id: Ia2fda3dff2f71d26726941a8be4ebd68a0cd9787
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl/+/25432
ci-image-build: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
Tested-by: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>
ci-image-boot-test: Jenkins Job builder account <agl-jobbuilder@automotivelinux.org>