leds: ss4200: Add depend on x86 arch

There is only one x86 hardware where the driver leds-ss4200 applies to.
Add kconfig dependency to x86 architecture, fix help text whitespace.

Signed-off-by: Martin Dummer <martin.dummer@gmx.net>
Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>