sh: Fix up the SH-3 build for recent TLB changes.

While the MMUCR.URB and ITLB/UTLB differentiation works fine for all SH-4
and later TLBs, these features are absent on SH-3. This splits out
local_flush_tlb_all() in to SH-4 and PTEAEX copies while restoring the
old SH-3 one, subsequently fixing up the build.

This will probably want some further reordering and tidying in the
future, but that's out of scope at present.

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