ARM: multi_v7_defconfig: Enable BACKLIGHT_CLASS_DEVICE

ARM: multi_v7_defconfig: Enable BACKLIGHT_CLASS_DEVICE

Commit 72fee6b0a3a4 ("fbdev: Restrict FB_SH_MOBILE_LCDC to SuperH")
disabled availablity of the SH_MOBILE_LCDC driver on the RENESAS arch.
This innocent change has a significant side-effect on the ARM's
multi_v7_defconfig, because FB_BACKLIGHT symbol is no longer selected,
what in turn leaves BACKLIGHT_CLASS_DEVICE symbol selected only as
a module. The latter disables some backlight related code in the DRM
core, because the DRM core is set to be compiled-in in this defconfig.
This leaves all DRM display panels without integrated backlight control,
even if the needed modules have been properly loaded and probed.

Fix this by selecting BACKLIGHT_CLASS_DEVICE to be compiled-in in
multi_v7_defconfig.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>