[MIPS] Fix build errors related to wbflush.h on tx4927/tx4938.

TX49 CPUs have a SYNC instruction so that CONFIG_CPU_HAS_WB is no
longer needed.

Signed-off-by: Atsushi Nemoto <anemo@mba.ocn.ne.jp>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
5 files changed