Blackfin: convert to GENERIC_HARDIRQS_NO__DO_IRQ

Blackfin already sets proper flow handlers on all IRQs, and we don't rely
on __do_IRQ, therefore we can simply select GENERIC_HARDIRQS_NO__DO_IRQ.

Signed-off-by: Michael Hennerich <michael.hennerich@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>