wil6210: add statistics for suspend time

Add statistics for total, min and max suspend time, that
calculates the time the 11ad device was in suspend.
Those statistics will help to estimate the power impact
of d3hot feature.

Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>