arm64: dts: ls1028a: Add Thermal Monitor Unit node

The Thermal Monitoring Unit (TMU) monitors and reports the
temperature from 2 remote temperature measurement sites
located on ls1028a chip.
Add TMU dts node to enable this feature.

Signed-off-by: Yuantian Tang <andy.tang@nxp.com>
Acked-by: Eduardo Valentin <edubezval@gmail.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>