Add support for exposing PCMs to userspace. PCMs are defined by topology
and the operations in this patch map to SOF IPC calls.

The .get_module_upon_open field is set to allow for module load/unload
tests. There is no risk of the sof-pci/acpi-dev module being removed
while the platform components are in use. This may need to be
revisited when DT platforms are supported.
Signed-off-by: Liam Girdwood <liam.r.girdwood@linux.intel.com>
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Mark Brown <broonie@kernel.org>