[ARM] 2884/1: BAST - fix PC104 IRQ routing

Patch from Ben Dooks

This has been broken for a while now, so fix the
problems with the code, test and bring up to date.
This also makes the code conditional on an
Kconfig option

Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>