PCI: add routines for debugging and handling lost interrupts

We're getting a lot of storage drivers blamed for interrupt misrouting
issues.  This patch provides a standard way of reporting the problem
... and, if possible, correcting it.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>