scsi: g_NCR5380: Use probe_irq_*() for IRQ probing

Use standard probe_irq_on() and probe_irq_off() functions instead of own
implementation.  This prevents warning messages like this in the kernel
log: genirq: Flags mismatch irq 1. 00000000 (NCR-probe) vs. 00000080
(i8042)

Move the IRQ trigger code from NCR5380 to g_NCR5380 where it is used.

Also clear interrupt flag before and after the probe.

Signed-off-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Ondrej Zary <linux@rainbow-software.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>