[BLOCK] Only include the compat ioctl code if CONFIG_BLOCK is set

Add an extra CONFIG_BLOCK_COMPAT that we can use in the Makefile

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/block/Makefile b/block/Makefile
index 3cfe7ce..8261081 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -11,4 +11,4 @@
 obj-$(CONFIG_IOSCHED_CFQ)	+= cfq-iosched.o
 
 obj-$(CONFIG_BLK_DEV_IO_TRACE)	+= blktrace.o
-obj-$(CONFIG_COMPAT)		+= compat_ioctl.o
+obj-$(CONFIG_BLOCK_COMPAT)	+= compat_ioctl.o