[PATCH] Alpha: ISA IRQs fixup for dp264

Basically, this extends original dp264 fixup to all dp264 variations.
Here is one minor change: mask out bits 4-7 of a value assigned by SRM,
because
- newer consoles report ISA IRQs with offset 0xe0;
- even if console IRQ value is bogus, we'll have a value < 16
  so it should be harmless as it won't clash with native IRQs.

Particularly this fixes USB interrupt problem on xp1000 and es40.

Signed-off-by: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>