swrast: rename texture fetch functions (pt. 1)

swrast: rename texture fetch functions (pt. 1)

Rename functions to match format names.

sed commands:
s/signed_rgba8888_rev/R8G8B8A8_SNORM/g
s/signed_rgba8888/A8B8G8R8_SNORM/g
s/f_rgba8888_rev/R8G8B8A_UNORM/g
s/f_rgba8888/A8B8G8R8_UNORM/g
s/f_rgbx8888_rev/R8G8B8X8_UNORM/g
s/f_rgbx8888/X8B8G8R8_UNORM/g
s/f_argb8888_rev/A8R8G8B8_UNORM/g
s/f_argb8888/B8G8R8A8_UNORM/g
s/f_xrgb8888_rev/X8R8G8B8_UNORM/g
s/f_xrgb8888/B8G8R8X8_UNORM/g
s/signed_rgbx8888/X8B8G8R8_SNORM/g

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>