intel/fs: Add more efficient fragment coordinate calculation.

intel/fs: Add more efficient fragment coordinate calculation.

The PIXEL_X/Y opcodes used by the current implementation are broken on
XeHP due to the new regioning restrictions of the floating-point pipe.
We could have the regioning lowering pass fix it in theory by lowering
the conversions into separate MOV instructions, but that would be more
costly than this implementation that only needs a pair of pipelined
ADDs and a pair of pipelined MOVs.

Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/10000>