rt2x00: Add queue statistics to debugfs

Rename "frame" folder to "queue" folder,
add extra file to this folder which contains
statistics about all hardware queues. This will
help debugging and spotting problems in the
queue indexing system.

Signed-off-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>