arm64: defconfig: CONFIG_DRM_ETNAVIV=m

For imx8 we want to enable etnaviv, let's enable it
in defconfig, it will be useful to have it enabled for KernelCI
boot and runtime testing.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>