ath5k: Update reset code

 * Update reset and sync with HALs

 * Clean up eeprom settings and tweaking of initvals and
   put them on separate functions

 * Set/Restore 32KHz ref clk operation

 * Add some more documentation

 TODO: Spur mitigation, tpc, half/quarter rate, compression etc

 v2: Address comments from Bob and Felix and fix RSSI threshold bug
 introduced on the first version of the patch

Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>

Signed-off-by: John W. Linville <linville@tuxdriver.com>