intel/fs: Use a pure vertical stride for large register strides

intel/fs: Use a pure vertical stride for large register strides

Register strides higher than 4 are uncommon but they can happen.  For
instance, if you have a 64-bit extract_u8 operation, we turn that into
UB -> UQ MOV with a source stride of 8.  Our previous calculation would
try to generate a stride of <32;8,8>:ub which is invalid because the
maximum horizontal stride is 4.  To solve this problem, we instead use a
stride of <8;1,0>.  As noted in the comment, this does not work as a
destination but that's ok as very few things actually generate that
stride.

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Cc: mesa-stable@lists.freedesktop.org