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/Makefile b/drivers/Makefile
index f2154e1..9d9f69a 100644
--- a/drivers/Makefile
+++ b/drivers/Makefile
@@ -59,7 +59,7 @@
 obj-$(CONFIG_SPL_USB_HOST) += usb/host/
 obj-$(CONFIG_OMAP_USB_PHY) += usb/phy/
 obj-$(CONFIG_SPL_SATA) += ata/ scsi/
-obj-$(CONFIG_HAVE_BLOCK_DEVICE) += block/
+obj-$(CONFIG_SPL_LEGACY_BLOCK) += block/
 obj-$(CONFIG_SPL_BLK) += block/
 obj-$(CONFIG_SPL_THERMAL) += thermal/