Current chv spec teels we can only use either 16 or 32 bits as precision.

Although in the past VLV went from 16/32 to 32/64 and spec might not be updated,
these precision values brings stability and fixes some issues Wayne was facing.

Cc: Wayne Boyer <wayne.boyer@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Tested-by: Wayne Boyer <wayne.boyer@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Sprinkle const as requested by Ville.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>