gpu: prefer 16bit floating point FBO formats to 16bit integer ones

According to earlier discussions, this can improve visual quality.
This only changes the preferred order of the formats, not the
formats themselves.

DOCS/man/options.rst

@@ -5005,9 +5005,12 @@ The following video options are currently all specific to ``--vo=gpu`` and
     Selects the internal format of textures used for FBOs. The format can
     influence performance and quality of the video output. ``fmt`` can be one
     of: rgb8, rgb10, rgb10_a2, rgb16, rgb16f, rgb32f, rgba12, rgba16, rgba16f,
-    rgba16hf, rgba32f. Default: ``auto``, which maps to rgba16 on desktop GL,
-    and rgba16f or rgb10_a2 on GLES (e.g. ANGLE), unless GL_EXT_texture_norm16
-    is available.
+    rgba16hf, rgba32f.
+
+    Default: ``auto``, which first attempts to utilize 16bit float
+    (rgba16f, rgba16hf), and falls back to rgba16 if those are not available.
+    Finally, attempts to utilize rgb10_a2 or rgba8 if all of the previous formats
+    are not available.
 
 ``--gamma-factor=<0.1..2.0>``
     Set an additional raw gamma factor (default: 1.0). If gamma is adjusted in