cpufreq: update to sysfs_emit() for safer buffer handling

cpufreq: update to sysfs_emit() for safer buffer handling

Replace sprintf() and scnprintf() with sysfs_emit() and sysfs_emit_at()
in the cpufreq core.

This ensures safer buffer handling and consistency with sysfs interfaces.

Update show_scaling_available_governors() and related functions for
compliance with the new API.

Signed-off-by: Perry Yuan <perry.yuan@amd.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20240619081520.259971-1-perry.yuan@amd.com
[ rjw: Changelog edits ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>