sh: Add SH7263 CPU support.

This adds support for the SH7263 (SH-2A) CPU.

This particular CPU is a superset of SH7203, adding some additional
peripheral blocks and hooking up additional (reserved on SH7203)
vectors in the INTC block.

No visibly nasty surprises, yet..

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