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/drivers/block/Makefile b/drivers/block/Makefile
index b221a7c..f48d3e1 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -6,7 +6,7 @@
 obj-$(CONFIG_$(SPL_)BLK) += blk-uclass.o
 
 ifndef CONFIG_$(SPL_)BLK
-obj-$(CONFIG_HAVE_BLOCK_DEVICE) += blk_legacy.o
+obj-$(CONFIG_SPL_LEGACY_BLOCK) += blk_legacy.o
 endif
 
 ifndef CONFIG_SPL_BUILD