x86/ioapic: Use legacy_pic to set correct gsi-irq mapping

x86/ioapic: Use legacy_pic to set correct gsi-irq mapping

Using compile time NR_LEGACY_IRQS causes the wrong gsi-irq
mapping on non-PC platforms, such as Moorestown. This patch uses
legacy_pic abstraction to set the correct number of legacy
interrupts at runtime. For Moorestown, nr_legacy_irqs = 0. We
have 1:1 mapping for gsi-irq even within the legacy irq range.

Signed-off-by: Jacob Pan <jacob.jun.pan@linux.intel.com>
Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
Link: http://lkml.kernel.org/n/tip-kzvj4xp9tmicuoqoh2w05iay@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@elte.hu>