asoc: add support run-time detection of Gen3/Gen4

On GVM, we need enable machine driver now for Gen3
and Gen4 in a image, which means we need detect dtb
file at run-time to register the soundcard of Gen3
and Gen4.

Change-Id: I9d8a5bb1f4c88616b90aea60d1bb5654b241d3d0
Signed-off-by: Deru Wang <deruwang@codeaurora.org>