[llvm-readelf][docs] Add missing options and details to the help output and the command guide

This change is to keep the help text and command guide of llvm-readelf
in tandem.

 - In the help text mention that --section-data, --section-relocations,
   --section-symbols and --stack-sizes have no effect on GNU style
   output; give the accepted values for --elf-output-style and update
   the description of --gnu-hash-table to use the command guide
   description.
 - In the command guide add the missing options -a,
   --dependant-libraries,--no-demangle, --wide and -W. Also update the
   description of --symbols so it matches the help text.

Differential Revision: https://reviews.llvm.org/D111240