Use #ifdef for IMAGE_BL* instead of #if

One nasty part of ATF is some of boolean macros are always defined
as 1 or 0, and the rest of them are only defined under certain
conditions.

For the former group, "#if FOO" or "#if !FOO" must be used because
"#ifdef FOO" is always true.  (Options passed by $(call add_define,)
are the cases.)

For the latter, "#ifdef FOO" or "#ifndef FOO" should be used because
checking the value of an undefined macro is strange.

Here, IMAGE_BL* is handled by make_helpers/build_macro.mk like
follows:

  $(eval IMAGE := IMAGE_BL$(call uppercase,$(3)))

  $(OBJ): $(2)
          @echo "  CC      $$<"
          $$(Q)$$(CC) $$(TF_CFLAGS) $$(CFLAGS) -D$(IMAGE) -c $$< -o $$@

This means, IMAGE_BL* is defined when building the corresponding
image, but *undefined* for the other images.

So, IMAGE_BL* belongs to the latter group where we should use #ifdef
or #ifndef.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/include/common/aarch32/el3_common_macros.S b/include/common/aarch32/el3_common_macros.S
index dcb4edd..463a080 100644
--- a/include/common/aarch32/el3_common_macros.S
+++ b/include/common/aarch32/el3_common_macros.S
@@ -228,7 +228,7 @@
 	 * ---------------------------------------------------------------------
 	 */
 	.if \_init_c_runtime
-#if IMAGE_BL32
+#ifdef IMAGE_BL32
 		/* -----------------------------------------------------------------
 		 * Invalidate the RW memory used by the BL32 (SP_MIN) image. This
 		 * includes the data and NOBITS sections. This is done to
@@ -253,7 +253,7 @@
 		bl	zeromem
 #endif
 
-#if IMAGE_BL1
+#ifdef IMAGE_BL1
 		/* -----------------------------------------------------
 		 * Copy data from ROM to RAM.
 		 * -----------------------------------------------------