Intel MID i2s: Reorganize mid_i2s driver headers

Intel MID i2s: Reorganize mid_i2s driver headers

BZ: 12606

The "intel_mid_i2s_if.h" header is now split in two:
 - intel_mid_i2s_if.h
 - intel_mid_i2s_common.h

The first one contains only the kernel API and associated structures except
intel_mid_i2s_settings, which is in intel_mid_i2s_common.h.  The latter also
contains the enums used (exclusively) in intel_mid_i2s_settings.  As the
"_common.h" header is to be used by the userspace, we also add it to the list of
headers to be exported.

It prepares the next commit that adds a test driver on top of this one.

Change-Id: I2011bfcabc1e86837843cd604328f17b24b7806e
Signed-off-by: David Wagner <davidx.wagner@intel.com>
Reviewed-on: http://android.intel.com:8080/27793
Reviewed-by: De Chivre, RenaudX <renaudx.de.chivre@intel.com>
Tested-by: Barthes, FabienX <fabienx.barthes@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>