scsi: aic7xxx: aic97xx: Remove FreeBSD-specific code

The file aic79xx_core.c still contains some FreeBSD-specific code/macro
guards, although cross-compatibility was in theory removed with commit
cca6cb8a

 ("scsi: aic7xxx: Fix build using bare-metal toolchain").
Remove it.

Link: https://lore.kernel.org/r/20200326193817.12568-1-alex.dewar@gmx.co.uk
Signed-off-by: Alex Dewar <alex.dewar@gmx.co.uk>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>