HID: nintendo: add support for md/gen 6B controller

The NSO MD/GEN 6B was a Japan-only controller released which has
6 buttons on the face of the controller. This adds support for this
controller. It still enumerates just like the 3B controller, but
will use extra bits in it's report for the 3 extra controllers. This
also changes the events reported to match the letter on the controller
for the NSO MD/GEN controller. The VID/PID it reports is the same as
the 3B controller.

This also removes a comment on the N64 Controllers which didn't
mean anything.

Signed-off-by: Ryan McClelland <rymcclel@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.com>