ath9k: Check allowed PCIE powersave configuration

When assigning the initvals for PCIE sleep/awake
registers, check the configuration that has been
assigned to pll_pwrsave during initialization. Also,
display a warning if we don't have valid arrays.

Signed-off-by: Sujith Manoharan <c_manoha@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>