Correct SPL uses of CMD_MMC

This converts 6 usages of this option to the non-SPL form, since there is
no SPL_CMD_MMC defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/rpi.h b/include/configs/rpi.h
index c3f8e7b..7c306cb 100644
--- a/include/configs/rpi.h
+++ b/include/configs/rpi.h
@@ -122,7 +122,7 @@
 	"fdt_addr_r=0x02600000\0" \
 	"ramdisk_addr_r=0x02700000\0"
 
-#if CONFIG_IS_ENABLED(CMD_MMC)
+#if IS_ENABLED(CONFIG_CMD_MMC)
 	#define BOOT_TARGET_MMC(func) \
 		func(MMC, mmc, 0) \
 		func(MMC, mmc, 1) \