common: Move and rename CONFIG_SYS_SUPPORT_64BIT_DATA

This is not really a CONFIG since it is not intended to be set by boards.
Move it into the compiler header with other similar defines, and rename
it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/command.c b/common/command.c
index ceca992..0d8bf24 100644
--- a/common/command.c
+++ b/common/command.c
@@ -469,7 +469,7 @@
 			return 2;
 		case 'l':
 			return 4;
-#ifdef CONFIG_SYS_SUPPORT_64BIT_DATA
+#ifdef MEM_SUPPORT_64BIT_DATA
 		case 'q':
 			return 8;
 #endif