cpu-topology: Move cpu topology code to common code.

Both RISC-V & ARM64 are using cpu-map device tree to describe
their cpu topology. It's better to move the relevant code to
a common place instead of duplicate code.

To: Will Deacon <will.deacon@arm.com>
To: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Atish Patra <atish.patra@wdc.com>
[Tested on QDF2400]
Tested-by: Jeffrey Hugo <jhugo@codeaurora.org>
[Tested on Juno and other embedded platforms.]
Tested-by: Sudeep Holla <sudeep.holla@arm.com>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Will Deacon <will.deacon@arm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>