x86/resctrl: Create helper for RMID allocation and mondata dir creation

When monitoring is supported, each monitor and control group is allocated an
RMID. For control groups, rdtgroup_mkdir_ctrl_mon() later goes on to allocate
the CLOSID.

MPAM's equivalent of RMID are not an independent number, so can't be allocated
until the CLOSID is known. An RMID allocation for one CLOSID may fail, whereas
another may succeed depending on how many monitor groups a control group has.

The RMID allocation needs to move to be after the CLOSID has been allocated.

Move the RMID allocation and mondata dir creation to a helper.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Reinette Chatre <reinette.chatre@intel.com>
Reviewed-by: Babu Moger <babu.moger@amd.com>
Tested-by: Peter Newman <peternewman@google.com>
Tested-by: Shaopeng Tan <tan.shaopeng@fujitsu.com>
Tested-by: Babu Moger <babu.moger@amd.com>
Tested-by: Carl Worth <carl@os.amperecomputing.com> # arm64
Link: https://lore.kernel.org/r/20240213184438.16675-4-james.morse@arm.com
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>