libvpx: Add VP9 decoder.

source/libvpx/vp9/common/ppc/vp9_copy_altivec.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.
+;
+
+
+    .globl copy_mem16x16_ppc
+
+;# r3 unsigned char *src
+;# r4 int src_stride
+;# r5 unsigned char *dst
+;# r6 int dst_stride
+
+;# Make the assumption that input will not be aligned,
+;#  but the output will be.  So two reads and a perm
+;#  for the input, but only one store for the output.
+copy_mem16x16_ppc:
+    mfspr   r11, 256            ;# get old VRSAVE
+    oris    r12, r11, 0xe000
+    mtspr   256, r12            ;# set VRSAVE
+
+    li      r10, 16
+    mtctr   r10
+
+cp_16x16_loop:
+    lvsl    v0,  0, r3          ;# permutate value for alignment
+
+    lvx     v1,   0, r3
+    lvx     v2, r10, r3
+
+    vperm   v1, v1, v2, v0
+
+    stvx    v1,  0, r5
+
+    add     r3, r3, r4          ;# increment source pointer
+    add     r5, r5, r6          ;# increment destination pointer
+
+    bdnz    cp_16x16_loop
+
+    mtspr   256, r11            ;# reset old VRSAVE
+
+    blr