We want to allow the caller the set any valid MOCS index as part of the
the intel_buf. Drop the MOCS enum in favour of raw mocs_index. Also drop
the getter/setter interface, for which there are no current callers for
the setter part. In the next patch we will expose the raw mocs_index.
Should be no functional changes here.

v2 (Zbigniew):
  - Rather just pass along UC directly to lower layers.

Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>
Reviewed-by: Zbigniew Kempczyński <zbigniew.kempczynski@intel.com>