x86, io_apic: Introduce x86_io_apic_ops.print_entries for debugging

This call-back is used to dump IO-APIC entries for debugging
purposes into the kernel log. VT-d needs a special routine
for this and will overwrite the default.

Signed-off-by: Joerg Roedel <joro@8bytes.org>
Acked-by: Sebastian Andrzej Siewior <sebastian@breakpoint.cc>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>