wil6210: more debug info for vring

print used/available counters on debugfs;
print to dmesg when Tx vring becomes empty

This aids with performance investigation

Change-Id: Idc8ae7190a50aafc6be81c970f50ae35060b2922
Signed-off-by: Vladimir Kondratiev <qca_vkondrat@qca.qualcomm.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Git-commit: 67c3e1b41efe4dd400f444c6dccc4538b627758c
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/linville/wireless-testing


Signed-off-by: Hamad Kadmany <hkadmany@codeaurora.org>