Add cpu aliases to U-Boot specific dtsi for hifive-unleashed.
Without aliases we see that the CPU device sequence numbers are set
randomly and the cpu list/detail command will show it as follows:
=> cpu list
1: cpu@1 rv64imafdc
2: cpu@2 rv64imafdc
3: cpu@3 rv64imafdc
0: cpu@4 rv64imafdc
Seems like CPU probing with dm-model also relies on aliases as observed
in case spi. The fu540-c000-u-boot.dtsi has cpu nodes and so adding
corresponding aliases we can ensure that cpu devices are assigned
proper sequence as follows:
=> cpu list
1: cpu@1 rv64imafdc
2: cpu@2 rv64imafdc
3: cpu@3 rv64imafdc
4: cpu@4 rv64imafdc