x86: I/O APIC: Include <asm/i8259.h> required by some code

Include <asm/i8259.h> for i8259A_lock used in print_PIC() -- #if-0-ed out
by default.  The 32-bit version gets it right already.

The plan is to enable this code with "apic=debug" eventually.  This will
aid with debugging strange problems without the need to ask people to
apply patches.

Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>