Reserve the top 16 flag bits for architecture-specific use

Add a convention that the generic global_data only occupy the bottom 16 bits
of the flags word, so that there is less chance of a conflict. At present the
x86 flags conflict.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>

include/asm-generic/global_data.h

@@ -104,7 +104,7 @@ typedef struct global_data {
 #endif
 
 /*
- * Global Data Flags
+ * Global Data Flags - the top 16 bits are reserved for arch-specific flags
  */
 #define GD_FLG_RELOC		0x00001	/* Code was relocated to RAM	   */
 #define GD_FLG_DEVINIT		0x00002	/* Devices have been initialized   */