brw: Don't assert about MAX_VGRF_SIZE in brw_opt_split_virtual_grfs()

This allows us to create temporary VGRFs that are larger than
MAX_VGRF_SIZE(devinfo), which will be split eventually.  They may not
be split on the initial pass, because we may need LOAD_PAYLOAD lowering,
copy propagation, and so on to occur first.  So we allow registers to
exceed that size initially.

The "Register allocation relies on split_virtual_grfs()" assertion in
brw_reg_allocate.cpp still asserts that all VGRFs which reach the
register allocator have been properly split.

One case where this is useful is for vectorizing convergent block loads.
We create temporaries to splat the SIMD1 values out to SIMD(N), which
can lead to some very large temporaries.  However, copy propagation and
so on ultimately eliminate these and they'll get split down to proper
sizes or elided entirely in the end.

(Note: both this and the prior commits from this merge request are
 needed to close the linked issue.)

Cc: mesa-stable
Reviewed-by: Matt Turner <mattst88@gmail.com>
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/12324
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/34461>

src/intel/compiler/brw_opt_virtual_grfs.cpp

@@ -114,7 +114,6 @@ brw_opt_split_virtual_grfs(brw_shader &s)
          if (split_points[reg]) {
             has_splits = true;
             vgrf_has_split[i] = true;
-            assert(offset <= MAX_VGRF_SIZE(s.devinfo));
             unsigned grf = brw_allocate_vgrf_units(s, offset).nr;
             for (unsigned k = reg - offset; k < reg; k++)
                new_virtual_grf[k] = grf;
@@ -126,7 +125,6 @@ brw_opt_split_virtual_grfs(brw_shader &s)
       }
 
       /* The last one gets the original register number */
-      assert(offset <= MAX_VGRF_SIZE(s.devinfo));
       s.alloc.sizes[i] = offset;
       for (unsigned k = reg - offset; k < reg; k++)
          new_virtual_grf[k] = i;