sh: Drop CPU subtype IRQ headers.

This drops the various IRQ headers that were floating around
and primarily providing hardcoded IRQ definitions for the
various CPU subtypes. This quickly got to be an unmaintainable
mess, made even more evident by the subtle breakage introduced
by the SH-2 and SH-2A changes.

Now that subtypes are able to register IRQ maps directly, just
rip all of the headers out.

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