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.

Change-Id: I14dfa206b141a4d2b5585d637fe94b2eed91d2b7
Signed-off-by: Maya Erez <qca_merez@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>
Git-commit: 262345265e599fe5ccc75ba435147d17df04bfd6
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


Signed-off-by: Maya Erez <merez@codeaurora.org>