[SCSI] libsas: make ATA functions selectable by a config option

Not everyone wants libsas automatically to pull in libata.  This patch
makes the behaviour configurable, so you can build libsas with or
without ATA support.

Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>
diff --git a/drivers/scsi/libsas/Makefile b/drivers/scsi/libsas/Makefile
index 6383eb5..fd387b9 100644
--- a/drivers/scsi/libsas/Makefile
+++ b/drivers/scsi/libsas/Makefile
@@ -33,5 +33,5 @@
 		sas_dump.o     \
 		sas_discover.o \
 		sas_expander.o \
-		sas_scsi_host.o \
-		sas_ata.o
+		sas_scsi_host.o
+libsas-$(CONFIG_SCSI_SAS_ATA) +=	sas_ata.o