i965/vec4: Move perf_debug about register spilling into the visitor.

i965/vec4: Move perf_debug about register spilling into the visitor.

This patch makes us only issue the performance warning about register
spilling if we actually spilled registers.  We also use scratch space
for indirect addressing and the like.

This is basically commit c51163b0cf7aff0375b1a5ea4cb3da9d9e164044 for
the vec4 backend.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>