staging: mt7621-dts: complete 'cpus' node

There are some properties missing in 'cpus' node for this SoC:
- '#address-cells'
- '#size-cells'
- 'device_type' and 'reg' in child cpu nodes.

Hence, add them all to the device tree file.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Link: https://lore.kernel.org/r/20211022095203.9343-1-sergio.paracuellos@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>