alpha: irq: remove deprecated use of IRQF_DISABLED

Interrupt handlers are always invoked with interrupts disabled, so
remove all uses of the deprecated IRQF_DISABLED flag.

Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Michael Cree <mcree@orcon.net.nz>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>