wil6210: add support for link statistics

Driver can request FW to report link statistics using
WMI_LINK_STATS_CMDID.
FW will report statistics with WMI_LINK_STATS_EVENTID.
Two categories of statistics defined: basic and global.

New "link_stats" debugfs is used for requesting basic statistics
report (write) and for reading the basic statistics (read).
"link_stats_global" debugfs is used for requesting and reading the
global statistics.

Change-Id: I45575baae44ee32fbe0ed655e0a36e63c2364142
Signed-off-by: Dedy Lansky <dlansky@codeaurora.org>
Signed-off-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Git-commit: 0c936b3c96337c3fd5ad4951ca7bdc54fa578a02
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/kvalo/ath.git


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