drivers: psci: remove cluster terminology and dependency on physical_package_id

Since the definition of the term "cluster" is not well defined in the
architecture, we should avoid using it. Also the physical package id
is currently mapped to so called "clusters" in ARM/ARM64 platforms which
is already argumentative.

Currently PSCI checker uses the physical package id assuming that CPU
power domains map to "clusters" and the physical package id in the code
as it stands also maps to cluster boundaries. It does that trying to
test "cluster" idle states to its best. However the CPU power domain
often but not always maps directly to the processor topology.

This patch removes the dependency on physical_package_id from the topology
in this PSCI checker. Also it replaces all the occurences of clusters to
cpu_groups which is derived from core_sibling_mask and may not directly
map to physical "cluster".

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>