i965/gen9: Enable rep clears on gen9
The (gen < 9) check in brw_clear() was too broad. It disabled all types
of fast color clears:
a. singlesample rep clears
b. singlesample MCS fast clears
c. multisample MCS fast clears
The MCS clears are still buggy, but the rep clear works well. So let's
enable it.
Reviewed-by:
Neil Roberts <neil@linux.intel.com>