arm64/mpam: resctrl: Add rmid file in resctrl sysfs

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

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rmid is used to mark each resctrl group for monitoring, anyhow, also
following corresponding resctrl group's configuration, we export rmid
sysfile to resctrl sysfs for any usage elsewhere such as SMMU io, user
can get rmid from a resctrl group and set this rmid to a target io
through SMMU driver if SMMU MPAM implemented, so make related io devices
can be monitored or accomplish aimed configuration for resource's usage.

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>