ncr5380: Remove more useless prototypes

Make use of the host template static initializer instead of assigning
handlers at run-time. Move __maybe_unused qualifiers from declarations
to definitions. Move the atari_scsi_bus_reset() wrapper after the
definition of NCR5380_bus_reset(). All of the host template handler
prototypes are now redundant so remove them.

The write_info() handler is only relevant to drivers using PSEUDO_DMA so
this patch fixes the compiler warning in atari_NCR5380.c and sun3_NCR5380.c:

  CC      drivers/scsi/atari_scsi.o
  drivers/scsi/NCR5380.h:329: warning: 'NCR5380_write_info' declared 'static' but never defined

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Tested-by: Michael Schmitz <schmitzmic@gmail.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>