arm_mpam: resctrl: Add rmid index helpers

maillist inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I8T2RT

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpam/snapshot/v6.7-rc2



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Because MPAM's pmg aren't identical to RDT's rmid, resctrl handles
some datastructrues by index. This allows x86 to map indexes to
RMID, and MPAM to map them to partid-and-pmg.

Add the helpers to do this.

Signed-off-by: James Morse <james.morse@arm.com>
Signed-off-by: Zeng Heng <zengheng4@huawei.com>