PCI: Disable AER with pci=nomsi

When booting with pci=nomsi aer causes lost interrupts and
lockdep inversions.

So check if MSIs are not disabled before initializing the aer
driver.

Signed-off-by: Andi Kleen <ak@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>