cpu/hotplug: Remove dependancy against cpu_primary_thread_mask

The commit 18415f33 ("cpu/hotplug: Allow "parallel" bringup up to
CPUHP_BP_KICK_AP_STATE") introduce a dependancy against a global variable
cpu_primary_thread_mask exported by the X86 code. This variable is only
used when CONFIG_HOTPLUG_PARALLEL is set.

Since cpuhp_get_primary_thread_mask() and cpuhp_smt_aware() are only used
when CONFIG_HOTPLUG_PARALLEL is set, don't define them when it is not set.

No functional change.

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/20230705145143.40545-2-ldufour@linux.ibm.com