thermal: intel: Use sysfs_emit() for powerclamp cpumask

cpumask_get() is used as a sysfs getter for the cpumask module
parameter. Use sysfs_emit() and cpumask_pr_args() to emit the mask.

This prepares for removing cpumap_print_to_pagebuf().

Signed-off-by: Yury Norov <ynorov@nvidia.com>
Link: https://patch.msgid.link/20260528183625.870813-16-ynorov@nvidia.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>