scsi: pm80xx: Deal with kexec reboots

A kexec reboot causes the controller fw to assert. This assertion shows up
in two ways, the controller doesn't show up as ready and an interrupt is
waiting as soon as the handler is registered. To resolve this added below
fix:

 - Split the interrupt handling setup into two parts, setup and request.

 - If the controller ready register indicates not-ready, but that the not
   readiness is only on the IOC units we can still try a reset to bring the
   system back to the pre-reboot state.

Link: https://lore.kernel.org/r/20200316074906.9119-3-deepak.ukey@microchip.com


Acked-by: Jack Wang <jinpu.wang@cloud.ionos.com>
Signed-off-by: Vikram Auradkar <auradkar@google.com>
Signed-off-by: Deepak Ukey <deepak.ukey@microchip.com>
Signed-off-by: Viswas G <Viswas.G@microchip.com>
Signed-off-by: Radha Ramachandran <radha@google.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>