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/doc/develop/driver-model/migration.rst b/doc/develop/driver-model/migration.rst
index 5a60436..742fea5 100644
--- a/doc/develop/driver-model/migration.rst
+++ b/doc/develop/driver-model/migration.rst
@@ -57,7 +57,7 @@
 appropriate DM driver, CONFIG_BLK needs to be set as well.  The final deadline
 here coincides with the final deadline for migration of the various block
 subsystems.  At this point we will be able to audit and correct the logic in
-Kconfig around using CONFIG_PARTITIONS and CONFIG_HAVE_BLOCK_DEVICE and make
+Kconfig around using CONFIG_PARTITIONS and CONFIG_SPL_LEGACY_BLOCK and make
 use of CONFIG_BLK / CONFIG_SPL_BLK as needed.
 
 CONFIG_DM_SPI / CONFIG_DM_SPI_FLASH