Patch from Petr Vandrovec <vandrove@vc.cvut.cz>

Recently I've observed problems with IDE disks while running UP kernel on
x86-64 - it complained a lot about lost irq from hda/hdc.  I tracked
problem down to the problem that at enable_irq() code calls
hw_resend_irq(), but on x86-64 hw_resend_irq() does something useful only
when CONFIG_SMP is defined, on UP systems it does nothing.

Due to this IRQ is lost - and when IDE retries command, it can again happen
that IRQ is delivered before IDE code does enable_irq(), and again and
again, unless due to drive being lazy finally once kernel does enable_irq()
before drive prepares its answer, and things move forward ...  to next lost
IRQ.
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>