cacheinfo: Add function to get cacheinfo for a given CPU and cache level

Resctrl open codes a search for information about a given cache level in
a couple of places (and more are on the way).

Provide a new inline function get_cpu_cacheinfo_level() in
<linux/cacheinfo.h> to do the search and return a pointer to the
cacheinfo structure.

Add lockdep_assert_cpus_held() to enforce the comment that cpuhp lock
must be held.

Simplify the existing get_cpu_cacheinfo_id() by using this new function
to do the search.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/20240610003927.341707-4-tony.luck@intel.com