CHROMIUM: ath10k: add debugfs support for aggr burst duration

This patch adds debugfs support for setting aggregation burst
duration for all access categories(VO, VI, BE, BK).

Burst duration takes values ranging from 0 to 8000 usecs and are set
using "burst_dur" debugfs entry.

BUG=b:131190756
TEST=echo "Be Bk Vi Vo" > /sys/kernel/debug/ieee80211/phyX/ath10k/burst_dur
Where Vo, Vi, Be, Bk corresponds to burst duration from 0-8000 usecs.

Change-Id: Ib1db633833279b2dc61d8e41d0a66365f22b78e0
Signed-off-by: Balaji Pothunoori <bpothuno@codeaurora.org>
Signed-off-by: Miaoqing Pan <miaoqing@codeaurora.org>
Signed-off-by: Bikshapathi Kothapeta <bkotha@codeaurora.org>
Reviewed-on: https://chromium-review.googlesource.com/1710154


Tested-by: Kan Yan <kyan@chromium.org>
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Kan Yan <kyan@chromium.org>