blk: Rename HAVE_BLOCK_DEVICE

This option is fact really related to SPL. For U-Boot proper we always use
driver model for block devices, so CONFIG_BLK is enabled if block devices
are in use.

It is only for SPL that we have two cases:

- SPL_BLK is enabled, in which case we use driver model and blk-uclass.c
- SPL_BLK is not enabled, in which case (if we need block devices) we must
  use blk_legacy.c

Rename the symbol to SPL_LEGACY_BLOCK to make this clear. This is
different enough from BLK and SPL_BLK that there should be no confusion.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/disk/disk-uclass.c b/disk/disk-uclass.c
index f3fb942..9351a5c 100644
--- a/disk/disk-uclass.c
+++ b/disk/disk-uclass.c
@@ -27,8 +27,7 @@
 	struct udevice *dev;
 	int ret;
 
-	if (!CONFIG_IS_ENABLED(PARTITIONS) ||
-	    !CONFIG_IS_ENABLED(HAVE_BLOCK_DEVICE))
+	if (!CONFIG_IS_ENABLED(PARTITIONS) || !blk_enabled())
 		return 0;
 
 	if (device_get_uclass_id(blk_dev) != UCLASS_BLK)