Fix usage of IMAGE_BLx macros

These macros are only defined for corresponding image,
and they are undefined for other images. It means that we have
to use ifdef or defined() instead of relying on being 0 by default.

Change-Id: Iad11efab9830ddf471599b46286e1c56581ef5a7
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>
diff --git a/plat/hisilicon/hikey/hikey_io_storage.c b/plat/hisilicon/hikey/hikey_io_storage.c
index 60ec42b..57c66d5 100644
--- a/plat/hisilicon/hikey/hikey_io_storage.c
+++ b/plat/hisilicon/hikey/hikey_io_storage.c
@@ -47,7 +47,7 @@
 
 static const io_block_dev_spec_t emmc_dev_spec = {
 	/* It's used as temp buffer in block driver. */
-#if IMAGE_BL1
+#ifdef IMAGE_BL1
 	.buffer		= {
 		.offset	= HIKEY_BL1_MMC_DATA_BASE,
 		.length	= HIKEY_BL1_MMC_DATA_SIZE,