scsi/NCR5380: remove unused BOARD_NORMAL and BOARD_NCR53C400

BOARD_NORMAL is completely unused and BOARD_NCR53C400 is used only by
g_NCR5380 internally. Remove the unused definitions.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Acked-by: Sam Creasey <sammy@sammy.net>
Signed-off-by: Christoph Hellwig <hch@lst.de>