Update MEM_SUPPORT_64BIT_DATA to be always defined

Define this macro always so we don't need the preprocessor to check it.
Convert the users to #if instead of #ifdef.

Note that '#if MEM_SUPPORT_64BIT_DATA' does not give an error if the
macro is not define. It just assumes zero.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stefan Roese <sr@denx.de>
diff --git a/common/command.c b/common/command.c
index 4f49f15..fc37ed4 100644
--- a/common/command.c
+++ b/common/command.c
@@ -473,7 +473,7 @@
 			return 2;
 		case 'l':
 			return 4;
-#ifdef MEM_SUPPORT_64BIT_DATA
+#if MEM_SUPPORT_64BIT_DATA
 		case 'q':
 			return 8;
 #endif