cpu/SMT: Store the current/max number of threads

Some architectures allow partial SMT states at boot time, ie. when not all
SMT threads are brought online.

To support that the SMT code needs to know the maximum number of SMT
threads, and also the currently configured number.

The architecture code knows the max number of threads, so have the
architecture code pass that value to cpu_smt_set_num_threads(). Note that
although topology_max_smt_threads() exists, it is not configured early
enough to be used here. As architecture, like PowerPC, allows the threads
number to be set through the kernel command line, also pass that value.

[ ldufour: Slightly reword the commit message ]
[ ldufour: Rename cpu_smt_check_topology and add a num_threads argument ]

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Laurent Dufour <ldufour@linux.ibm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Zhang Rui <rui.zhang@intel.com>
Link: https://lore.kernel.org/r/20230705145143.40545-5-ldufour@linux.ibm.com