x86/cpu/topology: Make primary thread mask available with SMP=n

x86/cpu/topology: Make primary thread mask available with SMP=n

cpu_primary_thread_mask is only defined when CONFIG_SMP=y. However, even
in UP kernels there is always exactly one CPU, which can reasonably be
treated as the primary thread.

Historically, topology_is_primary_thread() always returned true with
CONFIG_SMP=n. A recent commit:

  4b455f59945aa ("cpu/SMT: Provide a default topology_is_primary_thread()")

replaced it with a generic implementation with the note:

  "When disabling SMT, the primary thread of the SMT will remain
   enabled/active. Architectures that have a special primary thread (e.g.
   x86) need to override this function. ..."

For consistency and clarity, make the primary thread mask available
regardless of SMP, similar to cpu_possible_mask and cpu_present_mask.

Move __cpu_primary_thread_mask into common code to prevent build issues.
Let cpu_mark_primary_thread() configure the mask even for UP kernels,
alongside other masks. Then, topology_is_primary_thread() can
consistently reference it.

Signed-off-by: Chang S. Bae <chang.seok.bae@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Link: https://lore.kernel.org/r/20250320234104.8288-1-chang.seok.bae@intel.com