mac_scsi: Add module option to Kconfig

Allow mac_scsi to be built as a module. Replace the old validation of
__setup options with code that validates both module and __setup options.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Christoph Hellwig <hch@lst.de>
diff --git a/drivers/scsi/Kconfig b/drivers/scsi/Kconfig
index 3a820f6..60c67e1 100644
--- a/drivers/scsi/Kconfig
+++ b/drivers/scsi/Kconfig
@@ -1615,7 +1615,7 @@
 	  that leave the devices with SCSI operations partway completed.
 
 config MAC_SCSI
-	bool "Macintosh NCR5380 SCSI"
+	tristate "Macintosh NCR5380 SCSI"
 	depends on MAC && SCSI=y
 	select SCSI_SPI_ATTRS
 	help