vp8_loop_filter_bh_y_sse2: save/restore xmm registers

xmm[6-11] should be saved and restored for Windows x64; prevents an
encoder mismatch and some datarate issues.

Change-Id: I03c38eb18ec20c6c441cae19416393058baad1ee

vp8/common/x86/loopfilter_block_sse2.asm

@@ -150,6 +150,7 @@ sym(vp8_loop_filter_bh_y_sse2):
 
     push    rbp
     mov     rbp, rsp
+    SAVE_XMM 11
     push    r12
     push    r13
     mov     thresh, arg(4)
@@ -258,6 +259,7 @@ LF_FILTER xmm0, xmm1, xmm3, xmm8, xmm4, xmm2
 %ifidn __OUTPUT_FORMAT__,x64
     pop    r13
     pop    r12
+    RESTORE_XMM
     pop    rbp
 %endif