arm_mpam: [NFU] Rework ID remapping to use a kernel command-line argument

Hacking the source is an acceptable interface for experimentation,
but not very convenient.

Instead, add a kernel command-line parameter
mpam_partid_per_closid=<n> to specify how many PARTIDs are used to
provide monitoring groups for each resctrl CLOSID.

This change is not intended for upstream.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>