MIPS: configs: drop unused BACKLIGHT_GENERIC option

Commit 7ecdea4a ("backlight: generic_bl: Remove this driver as it is
unused") removed geenric_bl driver from the tree, together with
corresponding config option.

Remove BACKLIGHT_GENERIC config item from all MIPS configurations.

Fixes: 7ecdea4a

 ("backlight: generic_bl: Remove this driver as it is unused")
Signed-off-by: Andrey Zhizhikin <andrey.zhizhikin@leica-geosystems.com>
Reviewed-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>