powerpc/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 generic-64bit_defconfig.

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>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Cc: Sam Ravnborg <sam@ravnborg.org>
Link: https://lore.kernel.org/r/20201201222922.3183-6-andrey.zhizhikin@leica-geosystems.com'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/powerpc/configs/powernv_defconfig

@@ -208,7 +208,6 @@ CONFIG_FB_MATROX_G=y
 CONFIG_FB_RADEON=m
 CONFIG_FB_IBM_GXT4500=m
 CONFIG_LCD_PLATFORM=m
-CONFIG_BACKLIGHT_GENERIC=m
 # CONFIG_VGA_CONSOLE is not set
 CONFIG_LOGO=y
 CONFIG_HID_A4TECH=m