MLK-20964-2: arm64: defconfig: Make savedefconfig clean

There are differences between the output of `make savedefconfig` and the
arm64 defconfig. This happens because CONFIG_I2C_RPBUS=y depends on
CONFIG_RPMSG=y so the latter doesn't have to be explictly selected.

Fixes: b0ee196e ("MLK-20940-4 ARM64: defconfig: Add RPBUS and RPMSG config")

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Joakim Zhang <qiangqing.zhang@nxp.com>