ARM/leds: move ARM Versatile LED driver to leds subsystem

Now that we have converted this driver to a real platform device
module-based thing, we move the driver down into the LEDs
subsystem and rename the config option to LEDS_VERSATILE.

Cc: Richard Purdie <rpurdie@rpsys.net>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Pawel Moll <pawel.moll@arm.com>
Acked-by: Bryan Wu <cooloney@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>