x86/xsave: Make it clear that the XSAVE macros use (%edi)/(%rdi)

The XSAVE instruction family takes a memory argment.  The macros use
(%edi)/(%rdi) as that memory argument - make that clear to the reader.
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Link: http://lkml.kernel.org/r/1401387164-43416-7-git-send-email-fenghua.yu@intel.com

arch/x86/include/asm/xsave.h

@@ -52,6 +52,7 @@ extern void xsave_init(void);
 extern void update_regset_xstate_info(unsigned int size, u64 xstate_mask);
 extern int init_fpu(struct task_struct *child);
 
+/* These macros all use (%edi)/(%rdi) as the single memory argument. */
 #define XSAVE		".byte " REX_PREFIX "0x0f,0xae,0x27"
 #define XSAVEOPT	".byte " REX_PREFIX "0x0f,0xae,0x37"
 #define XSAVES		".byte " REX_PREFIX "0x0f,0xc7,0x2f"