Update libvpx snapshot to v0.9.7-p1 (Cayuga).

source/libvpx/vp8/encoder/x86/subtract_sse2.asm

 ;
 ;  Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 ;
 ;  Use of this source code is governed by a BSD-style license
 ;  that can be found in the LICENSE file in the root of the source
 ;  tree. An additional intellectual property rights grant can be found
 ;  in the file PATENTS.  All contributing project authors may
 ;  be found in the AUTHORS file in the root of the source tree.
 ;
 
@@ skipping 59 matching lines @@
     pop         rbp
     ret
 
 
 ;void vp8_subtract_mby_sse2(short *diff, unsigned char *src, unsigned char *pred, int stride)
 global sym(vp8_subtract_mby_sse2)
 sym(vp8_subtract_mby_sse2):
     push        rbp
     mov         rbp, rsp
     SHADOW_ARGS_TO_STACK 4
-    SAVE_XMM
+    SAVE_XMM 7
     GET_GOT     rbx
     push rsi
     push rdi
     ; end prolog
 
             mov         rsi,            arg(1) ;src
             mov         rdi,            arg(0) ;diff
 
             mov         rax,            arg(2) ;pred
             movsxd      rdx,            dword ptr arg(3) ;stride
@@ skipping 256 matching lines @@
     pop rsi
     RESTORE_GOT
     UNSHADOW_ARGS
     pop         rbp
     ret
 
 SECTION_RODATA
 align 16
 t80:
     times 16 db 0x80