ath9k_hw: dynamically choose the SERDES array for low power

The array we use will vary depending on whether or not we are
to go to lower power or not. The default values (iniPcieSerdes)
are a copy or what go into the registers through the INI files.

Cc: Aeolus Yang <aeolus.yang@atheros.com>
Cc: Madhan Jaganathan <madhan.jaganathan@atheros.com>
Signed-off-by: Luis R. Rodriguez <lrodriguez@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>