riscv: dts: starfive: add 'cpus' label to jh7110 and jh7100 soc dtsi

Add the 'cpus' label so that we can reference it in board dts files.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>