leds: Rename leds-cobalt driver

The leds-cobalt driver only supports the Coable Qube series
(not included in Cobalt Raq series).
Rename the driver and update Kconfig/Makefile.

Signed-off-by: Yoichi Yuasa <yoichi_yuasa@tripeaks.co.jp>
Acked-by: Florian Fainelli <florian.fainelli@telecomint.eu>
Signed-off-by: Richard Purdie <rpurdie@rpsys.net>