sh: Enable SH-X3 hardware synonym avoidance handling.

This enables support for the hardware synonym avoidance handling on SH-X3
CPUs for the case where dcache aliases are possible. icache handling is
retained, but we flip on broadcasting of the block invalidations due to
the lack of coherency otherwise on SMP.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>