x86/resctrl: Modify update_mba_bw() to use per CTRL_MON group event

x86/resctrl: Modify update_mba_bw() to use per CTRL_MON group event

update_mba_bw() hard codes use of the memory bandwidth local event which
prevents more flexible options from being deployed.

Change this function to use the event specified in the rdtgroup that is
being processed.

Mount time checks for the "mba_MBps" option ensure that local memory
bandwidth is enabled. So drop the redundant is_mbm_local_enabled() check.

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/20241206163148.83828-4-tony.luck@intel.com