rt2x00: Fix in_atomic() usage

rt73usb and rt2500usb used in_atomic to determine
if a configuration step should be rescheduled or not.
Since in_atomic() is not a valid method to determine
if sleeping is allowed we should fix the way this is handled
by adding a new flag to rt2x00.

In addition mark LED class support for the drivers broken
since that also uses the broken in_atomic() method but
so far no solution exists to have LED triggers work only
in scheduled context.

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