Revert "powerpc/topology: Update topology_core_cpumask"

Now that cpu_core_mask has been reintroduced, lets revert
commit 4bce5459

 ("powerpc/topology: Update topology_core_cpumask")

Post this commit, lscpu should reflect topologies as requested by a user
when a QEMU instance is launched with NUMA spanning multiple sockets.

Reported-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: Daniel Henrique Barboza <danielhb413@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210415120934.232271-3-srikar@linux.vnet.ibm.com