multi_v7_defconfig: make Rockchip DRM drivers built-in

These cause warnings in linux-next, as the symbols have become 'bool' there:

arch/arm/configs/multi_v7_defconfig:600:warning: symbol value 'm' invalid for ROCKCHIP_INNO_HDMI
arch/arm/configs/multi_v7_defconfig:599:warning: symbol value 'm' invalid for ROCKCHIP_DW_MIPI_DSI
arch/arm/configs/multi_v7_defconfig:598:warning: symbol value 'm' invalid for ROCKCHIP_DW_HDMI
arch/arm/configs/multi_v7_defconfig:597:warning: symbol value 'm' invalid for ROCKCHIP_ANALOGIX_DP

Signed-off-by: Arnd Bergmann <arnd@arndb.de>