rt2x00: Fix build errors due to modularized rfkill or leds and built-in rt2x00.

Fix by disabling rt2x00 rfkill support when rt2x00 is built-in and rfkill has been modularized, and
a similar scheme for the relationship between leds_class and rt2x00..
Also, give a warning to the end-user when rfkill-/leds-support is disabled this way, so that the
end-user has at least some clues on what is going on.

Proper fixing required some general updates of the Kconfig-structure for the rt2x00 driver, whereby
internal configuration symbols had to be moved to after the user-visible configuration symbols.

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