dm: blk: mmc: Tidy up some Makefile rules for SPL

Use the correct SPL_TPL_ variable so that these features can be enabled in
TPL and VPL as needed.

Disable it by default in TPL to avoid any code-size increase. No boards
are actually using it since the Makefile rules don't allow including
drivers/block/ with TPL_DM enabled. It can be manually enabled as needed.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jaehoon Chung <jh80.chung@samsung.com>
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index f48d3e1..19d9317 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -3,7 +3,7 @@
 # (C) Copyright 2000-2007
 # Wolfgang Denk, DENX Software Engineering, wd@denx.de.
 
-obj-$(CONFIG_$(SPL_)BLK) += blk-uclass.o
+obj-$(CONFIG_$(SPL_TPL_)BLK) += blk-uclass.o
 
 ifndef CONFIG_$(SPL_)BLK
 obj-$(CONFIG_SPL_LEGACY_BLOCK) += blk_legacy.o