backlight: generic-bl: Remove DRIVER1 state

Nothing in the entire tree ever sets this, which means this is dead
code. Remove it.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>