fs/resctrl: Add event configuration directory under info/L3_MON/

fs/resctrl: Add event configuration directory under info/L3_MON/

The "mbm_event" counter assignment mode allows the user to assign a hardware
counter to an RMID, event pair and monitor the bandwidth as long as it is
assigned. The user can specify the memory transaction(s) for the counter to
track.

When this mode is supported, the /sys/fs/resctrl/info/L3_MON/event_configs
directory contains a sub-directory for each MBM event that can be assigned to
a counter.  The MBM event sub-directory contains a file named "event_filter"
that is used to view and modify which memory transactions the MBM event is
configured with.

Create /sys/fs/resctrl/info/L3_MON/event_configs directory on resctrl mount
and pre-populate it with directories for the two existing MBM events:
mbm_total_bytes and mbm_local_bytes. Create the "event_filter" file within
each MBM event directory with the needed *show() that displays the memory
transactions with which the MBM event is configured.

Example:
  $ mount -t resctrl resctrl /sys/fs/resctrl
  $ cd /sys/fs/resctrl/
  $ cat info/L3_MON/event_configs/mbm_total_bytes/event_filter
    local_reads,remote_reads,local_non_temporal_writes,
    remote_non_temporal_writes,local_reads_slow_memory,
    remote_reads_slow_memory,dirty_victim_writes_all

  $ cat info/L3_MON/event_configs/mbm_local_bytes/event_filter
    local_reads,local_non_temporal_writes,local_reads_slow_memory

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/cover.1757108044.git.babu.moger@amd.com