qla2xxx: Collect PCI register checks and board_disable scheduling

Add an uint16_t variant of qla2x00_check_reg_for_disconnect and use
these routines to check and schedule a PCI-disconnected board from a
centralized place.

Signed-off-by: Joe Lawrence <joe.lawrence@stratus.com>
Acked-by: Chad Dupuis <chad.dupuis@qlogic.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>