ptn: Fix all users of ptn_swizzle

ptn: Fix all users of ptn_swizzle

None of the callers actually wanted what it did.  In ptn_xpd, you only
ever want a vec3 swizzle.  In ptn_tex, you want a swizzle that matches
the number of required texture coordinates.

shader-db results:

G45:
total instructions in shared programs: 4011240 -> 4010911 (-0.01%)
instructions in affected programs: 59232 -> 58903 (-0.56%)
helped: 114
HURT: 0

total cycles in shared programs: 84314194 -> 84313220 (-0.00%)
cycles in affected programs: 779150 -> 778176 (-0.13%)
helped: 110
HURT: 13

Ironlake:
total instructions in shared programs: 6397262 -> 6396605 (-0.01%)
instructions in affected programs: 117402 -> 116745 (-0.56%)
helped: 227
HURT: 0

total cycles in shared programs: 128889798 -> 128888524 (-0.00%)
cycles in affected programs: 1214644 -> 1213370 (-0.10%)
helped: 179
HURT: 44

Sandy Bridge:
total instructions in shared programs: 8467391 -> 8467384 (-0.00%)
instructions in affected programs: 3107 -> 3100 (-0.23%)
helped: 10
HURT: 6

total cycles in shared programs: 117580120 -> 117573448 (-0.01%)
cycles in affected programs: 103158 -> 96486 (-6.47%)
helped: 84
HURT: 11

Ivy Bridge:
total instructions in shared programs: 7774255 -> 7774258 (0.00%)
instructions in affected programs: 1677 -> 1680 (0.18%)
helped: 8
HURT: 6

total cycles in shared programs: 65743828 -> 65739190 (-0.01%)
cycles in affected programs: 89312 -> 84674 (-5.19%)
helped: 78
HURT: 23

Haswell:
total instructions in shared programs: 7107172 -> 7107150 (-0.00%)
instructions in affected programs: 2048 -> 2026 (-1.07%)
helped: 16
HURT: 0

total cycles in shared programs: 64653636 -> 64647486 (-0.01%)
cycles in affected programs: 86836 -> 80686 (-7.08%)
helped: 85
HURT: 17

Broadwell and Skylake:
total instructions in shared programs: 8447529 -> 8447507 (-0.00%)
instructions in affected programs: 2038 -> 2016 (-1.08%)
helped: 16
HURT: 0

total cycles in shared programs: 66418670 -> 66413416 (-0.01%)
cycles in affected programs: 90110 -> 84856 (-5.83%)
helped: 83
HURT: 20

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>