logcat: clean up handling of logd control commands with -f and -L

* Print an error if -c is provided with -f and -L since it is ambiguous
* Move the clear operation when -f is provided to a stand alone
  location, since there is no need to loop
* Prevent -g/-G, -S, and -p/-P with -f, since that combination doesn't
  make sense

Test: logpersist works
Change-Id: I6d8709bd61c898c47835470e99b0acff8c2692e4