i965: Fix textureGather with RG32I/UI on Gen7.

i965: Fix textureGather with RG32I/UI on Gen7.

According to the "Gather4 R32G32_FLOAT Bug" internal documentation
page, the R32G32_UINT and R32G32_SINT formats are affected by the
same bug as R32G32_FLOAT.  Applying the same workarounds should be
viable - apparently the R32G32_FLOAT_LD format shouldn't corrupt
integer data which is NaN or other sketchy floating point values.

One irritating caveat is that, because it's a FLOAT format, the
alpha channel or any set to SCS_ONE return 0x3f8 (1.0) rather than
integer 1.  So we need shader code to whack those channels to 1.

Fixes GL45-CTS.texture_gather.plain-gather-int-cube-rg on Haswell.

v2: Fix swizzle component zeroing (caught by Jordan Justen).

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>