staging: greybus: Kconfig: enable possibility to select light driver

Remove BROKEN keyword to allow the light driver to be select now that
we fixed the kernel version dependencies. Also fix the module name in
the help section.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>