"altmask" means the field is principally a bitmask of bits from the
enum, but in some cases can obtain other values (e.g. "out-of-band" data
in a free bit).
Several fields in xinput will benefit from this extra metadata.
Suggested-by: Peter Harris <pharris@opentext.com>
Signed-off-by: Ran Benita <ran234@gmail.com>
Signed-off-by: Peter Harris <pharris@opentext.com>