Add MSA optimized YUY2ToI422, YUY2ToI420, UYVYToI422, UYVYToI420 functions

docs/getting_started.md

 # Getting Started
 
 How to get and build the libyuv code.
 
 ## Pre-requisites
 
 You'll need to have depot tools installed: https://www.chromium.org/developers/how-tos/install-depot-tools
 Refer to chromium instructions for each platform for other prerequisites.
 
 ## Getting the Code
@@ skipping 148 matching lines @@
 ia32
 
     gn gen out/Release "--args=is_debug=false target_os=\"android\" target_cpu=\"x86\""
     gn gen out/Debug "--args=is_debug=true target_os=\"android\" target_cpu=\"x86\""
     ninja -j7 -v -C out/Debug libyuv_unittest
     ninja -j7 -v -C out/Release libyuv_unittest
 
 mipsel
 
     gn gen out/Release "--args=is_debug=false target_os=\"android\" target_cpu=\"mipsel\" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
-    gn gen out/Debug "--args=is_debug=true target_os=\"android\" target_cpu=\"mipsel\"" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
+    gn gen out/Debug "--args=is_debug=true target_os=\"android\" target_cpu=\"mipsel\" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
     ninja -j7 -v -C out/Debug libyuv_unittest
     ninja -j7 -v -C out/Release libyuv_unittest
 
-    gn gen out/Release "--args=is_debug=false target_os=\"android\" target_cpu=\"mips64el\"" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
-    gn gen out/Debug "--args=is_debug=true target_os=\"android\" target_cpu=\"mips64el\"" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
+    gn gen out/Release "--args=is_debug=false target_os=\"android\" target_cpu=\"mips64el\" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
+    gn gen out/Debug "--args=is_debug=true target_os=\"android\" target_cpu=\"mips64el\" mips_arch_variant=\"r6\" mips_use_msa=true is_component_build=true is_clang=false"
     ninja -j7 -v -C out/Debug libyuv_unittest
     ninja -j7 -v -C out/Release libyuv_unittest
 
 arm disassembly:
 
     third_party/android_tools/ndk/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin/aarch64-linux-android-objdump -d ./out/Release/obj/libyuv/row_common.o >row_common.txt
 
     third_party/android_tools/ndk/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin/aarch64-linux-android-objdump -d ./out/Release/obj/libyuv_neon/row_neon.o >row_neon.txt
 
     third_party/android_tools/ndk/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin/aarch64-linux-android-objdump -d ./out/Release/obj/libyuv_neon/row_neon64.o >row_neon64.txt
@@ skipping 88 matching lines @@
     gn gen out/Debug "--args=is_debug=true is_asan=true"
     ninja -j7 -v -C out/Debug
 
     Sanitizers available: tsan, msan, asan, ubsan, lsan
 
 ### Running Dr Memory memcheck for Windows
 
 Pre-requisite: Install Dr Memory for Windows and add it to your path: http://www.drmemory.org/docs/page_install_windows.html
 
     drmemory out\Debug\libyuv_unittest.exe --gtest_catch_exceptions=0 --gtest_filter=*