ath5k: Reset cleanup and generic cleanup

ath5k: Reset cleanup and generic cleanup

 * No functional changes

 * Clean up reset:
 Introduce init functions for each unit and call them instead
 of having everything inside ath5k_hw_reset (it's just c/p for
 now so nothing changes except calling order -I tested it with
 various cards and it's ok-)

 * Further cleanups:
 ofdm_timings belongs to phy.c
 rate_duration belongs to pcu.c
 clock functions are general and belong to reset.c (more to follow)

 * Reorder functions for better organization:
 We start with helpers and other functions follow in categories,
 init functions are last

 Signed-off-by: Nick Kossifidis <mickflemm@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>