ARM: shmobile: defconfig: Refresh for v5.9-rc1

Refresh the defconfig for Renesas ARM systems:
  - Drop CONFIG_BACKLIGHT_GENERIC=n (removed in commit 7ecdea4a
    ("backlight: generic_bl: Remove this driver as it is unused")).
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20200819101125.12113-1-geert+renesas@glider.be

arch/arm/configs/shmobile_defconfig

@@ -136,7 +136,6 @@ CONFIG_DRM_SIMPLE_BRIDGE=y
 CONFIG_DRM_I2C_ADV7511=y
 CONFIG_DRM_I2C_ADV7511_AUDIO=y
 CONFIG_FB_SH_MOBILE_LCDC=y
-# CONFIG_BACKLIGHT_GENERIC is not set
 CONFIG_BACKLIGHT_PWM=y
 CONFIG_BACKLIGHT_AS3711=y
 CONFIG_SOUND=y