Swizzle format:

7:6 5:4 3:2 1:0
w z y x

16 bit format:

SwzCAM (15..13) (12..8) (7..0)
0 rsvd0 regidx0 swiz0
1 rsvd1 regidx1 swiz1
2 rsvd2 regidx2 swiz2
3 rsvd3 regidx3 swiz3