ARM: OMAP2: fix omap3 touchbook kconfig warning

warning: (MACH_OMAP3_TOUCHBOOK && DRM_RADEON_KMS && DRM_I915 &&
STUB_POULSBO && FB_BACKLIGHT && USB_APPLEDISPLAY && FB_OLPC_DCON &&
ASUS_LAPTOP && SONY_LAPTOP && THINKPAD_ACPI && EEEPC_LAPTOP &&
ACPI_ASUS && ACPI_CMPC && SAMSUNG_Q10) selects BACKLIGHT_CLASS_DEVICE
which has unmet direct dependencies (HAS_IOMEM && BACKLIGHT_LCD_SUPPORT)

A lot of boards need BACKLIGHT_CLASS_DEVICE for the framebuffers to
work, but it's not *needed* for the device itself. It might be nice to
enable it by default somewhoe if graphics stuff is enabled, but that's
another story.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>