sched: Centralize SCHED_{SMT, MC, CLUSTER} definitions

Barry recently introduced a new CONFIG_SCHED_CLUSTER, and discussions
around that highlighted that every architecture redefines its own help text
and dependencies for CONFIG_SCHED_SMT and CONFIG_SCHED_MC.

Move the definition of those to scheduler's Kconfig to centralize help text
and generic dependencies (i.e. SMP). Make them depend on a matching
ARCH_SUPPORTS_SCHED_* which the architectures can select with the relevant
architecture-specific dependency.

s390 uses its own topology table (set_sched_topology()) and doesn't seem to
cope without SCHED_MC or SCHED_SMT, so those remain untogglable.

Suggested-by: Barry Song <21cnbao@gmail.com>
Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>