cpupower: Unify cpupower-frequency-* manpages

cpupower-frequency-* manpages slightly differed from the others.
  - Use uppercase letters in the title
  - Show cpupower Manual in the header
  - Remove Mattia from left down corner of the manpage, he is already
    listed as author
  - Remove --help, prints this message -> not needed

Signed-off-by: Thomas Renninger <trenn@suse.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>