platform/x86: Remove left-over BACKLIGHT_LCD_SUPPORT

The CONFIG_BACKLIGHT_LCD_SUPPORT was removed in commit 8c5dc8d9
("video: backlight: Remove useless BACKLIGHT_LCD_SUPPORT kernel
symbol"). Options protected by CONFIG_BACKLIGHT_LCD_SUPPORT are now
available directly.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>