[SCSI] aic7xxx: fix warnings with CONFIG_PM disabled

  CC [M]  drivers/scsi/aic7xxx/aic7xxx_osm_pci.o
drivers/scsi/aic7xxx/aic7xxx_osm_pci.c:148: warning: 'ahc_linux_pci_dev_suspend' defined but not used
drivers/scsi/aic7xxx/aic7xxx_osm_pci.c:166: warning: 'ahc_linux_pci_dev_resume' defined but not used

This moves aic7xxx_pci_driver struct, removes some forward declarations,
and adds some ifdef CONFIG_PM.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>