v2: Fix size/type mask to properly handle 8-bit types.
v3: Add helpers to get the bitsize and base type of a
nir_alu_type enum.
Signed-off-by: Juan A. Suarez Romero <jasuarez@igalia.com> Reviewed-by: Jason Ekstrand <jason@jlekstrand.net> Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com> Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>