backlight: Remove ld9040 driver

The driver for LD9040 AMOLED LCD panel was superseded with DRM driver
panel-samsung-ld9040.c.  It does not support DeviceTree and respective
possible user (Exynos4210 Universal C210) is DeviceTree-only and uses
DRM version of driver.

Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Acked-by: Jingoo Han <jingoohan1@gmail.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>