Documentation/x86: Update resctrl.rst for new features

Update the documentation for the new features:

1. Slow Memory Bandwidth allocation (SMBA).

   With this feature, the QOS enforcement policies can be applied to the
   external slow memory connected to the host. QOS enforcement is accomplished
   by assigning a Class Of Service (COS) to a processor and specifying
   allocations or limits for that COS for each resource to be allocated.

2. Bandwidth Monitoring Event Configuration (BMEC).

   The bandwidth monitoring events mbm_total_bytes and mbm_local_bytes are set
   to count all the total and local reads/writes respectively.  With the
   introduction of slow memory, the two counters are not enough to count all the
   different types of memory events. With the feature BMEC, the users have the
   option to configure mbm_total_bytes and mbm_local_bytes to count the specific
   type of events.

Also add configuration instructions with examples.

Signed-off-by: Babu Moger <babu.moger@amd.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/20230113152039.770054-14-babu.moger@amd.com