sh: Fix up the SH-3 build.

SH-3 lacks an MMUCR_TI definition for global TLB flushes. As SH-3 parts
lack a split TLB, the same global flush behaviour is accomplished
through the flush bit, which just happens to be the same as on SH-4.

This fixes up the build for all SH-3 MMU parts.

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