ath6kl: Implement support for power parameter control from userspace

In order to allow user space based control of power parameters, we use
available debugfs infrastructure. With these features user can control
power consumption by adjusting various sleep/wake up related parameters.
The feature has been added for testing purposes. All 5 parameters are
mandatory in correct order. They have to be written to the power_params
file. These are:

1) idle_period
2) no_of_pspoll
3) dtim_policy
4) tx_wakeup_policy
5) no_tx_to_wakeup

Example:

echo "200 1 0 1 1" > power_params

Signed-off-by: Rishi Panjwani <rpanjwan@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>