add comments about copyright for the code from mpv

wm4 says the table va_to_imgfmt in commit 479e57a is copied from mpv. That file is under GPL.  So I revert to the `switch...case...` style.
ass_to_plaintext() is confirmed can be under LGPL.

src/codec/video/VideoDecoderVAAPI.cpp

@@ -167,24 +167,19 @@ struct fmtentry {
     uint32_t va;
     VideoFormat::PixelFormat fmt;
 };
-static const struct fmtentry va_to_imgfmt[] = {
-    {VA_FOURCC_NV12, VideoFormat::Format_NV12},
-    {VA_FOURCC_YV12,  VideoFormat::Format_YUV420P},
-    {VA_FOURCC_IYUV, VideoFormat::Format_YUV420P},
-    {VA_FOURCC_UYVY, VideoFormat::Format_UYVY},
-    {VA_FOURCC_YUY2, VideoFormat::Format_YUYV},
-    // Note: not sure about endian issues
-    {VA_FOURCC_RGBA, VideoFormat::Format_RGB32},
-    {VA_FOURCC_RGBX, VideoFormat::Format_RGB32},
-    {VA_FOURCC_BGRA, VideoFormat::Format_RGB32},
-    {VA_FOURCC_BGRX, VideoFormat::Format_RGB32},
-    {0             , VideoFormat::Format_Invalid}
-};
+
 VideoFormat::PixelFormat pixelFormatFromVA(uint32_t fourcc)
 {
-    for (const struct fmtentry *entry = va_to_imgfmt; entry->va; ++entry) {
-        if (entry->va == fourcc)
-            return entry->fmt;
+    switch (fourcc) {
+    case VA_FOURCC_NV12:
+        return VideoFormat::Format_NV12;
+    case VA_FOURCC_YV12:
+    case VA_FOURCC_IYUV:
+        return VideoFormat::Format_YUV420P;
+    case VA_FOURCC_UYVY:
+        return VideoFormat::Format_UYVY;
+    default:
+        return VideoFormat::Format_Invalid;
     }
     return VideoFormat::Format_Invalid;
 }

src/subtitle/PlainText.cpp

@@ -27,7 +27,10 @@
 namespace QtAV {
 namespace PlainText {
 
-// from mpv/sub/sd_ass.c
+/*
+ *  from mpv/sub/sd_ass.c
+ * ass_to_plaintext() was written by wm4 and he says it can be under LGPL
+ */
 
 struct buf {
     char *start;

src/vaapi/SurfaceInteropVAAPI.cpp

@@ -1,6 +1,6 @@
 /******************************************************************************
     QtAV:  Media play library based on Qt and FFmpeg
-    Copyright (C) 2014-2015 Wang Bin <[email protected]>
+    Copyright (C) 2014-2016 Wang Bin <[email protected]>
 
 *   This file is part of QtAV
 
@@ -18,6 +18,8 @@
     License along with this library; if not, write to the Free Software
     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301  USA
 ******************************************************************************/
+/// The EGL+DMA part is from mpv and under LGPL
+
 #include "SurfaceInteropVAAPI.h"
 #ifndef QT_NO_OPENGL
 #include "utils/OpenGLHelper.h"