tools/power/cpupower: Add documentation for some recently introduced options

The 'cpupower-set' tool has been enhanced with new features:

  commit f2ab5557 ("cpupower: Add EPP value change support")
  commit df8776b0 ("cpupower: Add support for amd_pstate mode change")
  commit eb426fc6 ("cpupower: Add turbo-boost support in cpupower")

However, the corresponding manpage was never updated.

Add a basic description of these new options to the existing manpage.

Commit description updated to fix checkpatch errors: Shuah Khan

Signed-off-by: Tor Vic <torvic9@mailbox.org>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>