CCodec: move Buffers out into a separate file

Seperate Buffers out before we add complex logic to them. Also add
missing documentation.

Bug: 130223947
Test: builds
Change-Id: I8f992cb36499401ee2c6d729aa52f3888a7bcea5
diff --git a/media/codec2/sfplugin/Android.bp b/media/codec2/sfplugin/Android.bp
index 66457e7..8ae80ee 100644
--- a/media/codec2/sfplugin/Android.bp
+++ b/media/codec2/sfplugin/Android.bp
@@ -5,6 +5,7 @@
         "C2OMXNode.cpp",
         "CCodec.cpp",
         "CCodecBufferChannel.cpp",
+        "CCodecBuffers.cpp",
         "CCodecConfig.cpp",
         "Codec2Buffer.cpp",
         "Codec2InfoBuilder.cpp",