ABI: sysfs-bus-usb: add missing sysfs fields

There are lots of interface, power and endpoint properties that are currently
missing any documentation.

Add a description for them.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/7f6f7b955032836546f78a9041b22c10b6f4bc5b.1632750608.git.mchehab+huawei@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>