arm64: dts: imx8mm-verdin: add single-master property to all i2c nodes

By default we expect all i2c nodes to be single-master, we do not have
any module or carrier board that uses multi-master mode on any i2c
controller. With this property set, we benefit from optimisations made
exclusively for single-masters.

Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>