x86/resctrl: Update documentation with Sub-NUMA cluster changes

x86/resctrl: Update documentation with Sub-NUMA cluster changes

With Sub-NUMA Cluster (SNC) mode enabled, the scope of monitoring resources
is per-NODE instead of per-L3 cache. Backwards compatibility is maintained
by providing files in the mon_L3_XX directories that sum event counts
for all SNC nodes sharing an L3 cache.

New files provide per-SNC node event counts.

Users should be aware that SNC mode also affects the amount of L3 cache
available for allocation within each SNC node.

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>
Tested-by: Babu Moger <babu.moger@amd.com>
Link: https://lore.kernel.org/r/20240628215619.76401-20-tony.luck@intel.com