sh: intc: Make ack_regs generally available.

Currently this is ifdef'ed under SH-3 and SH-4A, but there are other CPUs
that will need this as well. Given the size of the existing data
structures, this doesn't cause any additional cacheline utilization for
the existing users, so has no direct impact on the data structures.

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