options: add --hwdec=yes as alias for --hwdec=auto

This also lets you just do "mpv --hwdec file.mkv", with the minor caveat
that the legacy syntax "--hwdec val" or "-hwdec val" (without "=") does
not work as expected anymore.

DOCS/man/options.rst

@@ -591,8 +591,9 @@ Video
     ``<api>`` can be one of the following:
 
     :no:        always use software decoding (default)
-    :auto:      see below
-    :auto-copy: see below
+    :auto:      enable best hw decoder (see below)
+    :yes:       exactly the same as ``auto``
+    :auto-copy: enable best hw decoder with copy-back (see below)
     :vdpau:     requires ``--vo=vdpau`` or ``--vo=opengl`` (Linux only)
     :vaapi:     requires ``--vo=opengl`` or ``--vo=vaapi`` (Linux only)
     :vaapi-copy: copies video back into system RAM (Linux with Intel GPUs only)

options/options.c

@@ -86,6 +86,7 @@ extern const struct m_obj_list ao_obj_list;
 const struct m_opt_choice_alternatives mp_hwdec_names[] = {
     {"no",          HWDEC_NONE},
     {"auto",        HWDEC_AUTO},
+    {"yes" ,        HWDEC_AUTO},
     {"auto-copy",   HWDEC_AUTO_COPY},
     {"vdpau",       HWDEC_VDPAU},
     {"videotoolbox",HWDEC_VIDEOTOOLBOX},