arm64/mpam: Add helper for getting mpam sysprops

hulk inclusion
category: feature
feature: ARM MPAM support
bugzilla: 48265
CVE: NA

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Now mpam sysprops have been probed, maximum support of partid
and pmg should be exported to resctrl.

For MPAM, Processing elements (PEs) issue memory-system requests,
PEs must implement the MPAMn_ELx registers and their behaviors to
generate the PARTID and PMG fields of memory-system requests.

For resctrl, partid and pmg should be used to combined into a unique
rmid for labeling each group, and partid for determining the maximum
number of ctrl groups.

Signed-off-by: Wang ShaoBo <bobo.shaobowang@huawei.com>
Reviewed-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Reviewed-by: Cheng Jian <cj.chengjian@huawei.com>
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>