ath9k: Read and write the TSF via debugfs

This patch adds an ath9k specific entry to read, write and reset the TSF into the debugfs, like in ath5k. This makes debugging the IBSS handling of wifi drivers _much_ easier.

Signed-off-by: Alina Friedrichsen <x-alina@gmx.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>