doc/encoders: fix the misleading usage of profile

users are getting mislead by the integer, although profile
can support both const string and integer.
http://ffmpeg.org/pipermail/ffmpeg-user/2020-June/049025.html

Also fix the order of high and main, it's not my intention.

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>

doc/encoders.texi

@@ -2740,17 +2740,17 @@ MPEG-2 video encoder.
 @subsection Options
 
 @table @option
-@item profile @var{integer}
+@item profile
 Select the mpeg2 profile to encode:
 
 @table @samp
 @item 422
-@item main
+@item high
 @item ss
 Spatially Scalable
 @item snr
 SNR Scalable
-@item high
+@item main
 @item simple
 @end table