mpt2sas: make watchdog instantiated device removal safe

Calling pci_stop_and_remove_bus_device from a SCSI LLD may introduce
device removal races with PCI callback functions.

Simplify the driver's watchdog mechanism by separating PCI device
removal from SCSI midlayer detachment. When the watchdog wishes to
remove a SCSI device from the topology, detach from the SCSI midlayer,
leaving the PCI device alone.  Adjust various pci_driver callbacks to
account for a potentially SCSI detached PCI device.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
mpt2sas: don't print watchdog msg until EEH recovery has failed

The watchdog routine allows a few iterations for PCI EEH recovery to
potentially resolve PCI bus errors. Don't display the "SAS host is
non-operational" message during this grace period.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>