arm64/mpam: Allocate new partid for the created ctrl group

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I9ARW6



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When a new ctrl group is created under root group, it needs to allocate
a new partid for that.

After that, the piece of code also needs to make refactoring indeed.

Fixes: a8c87e34 (arm64/mpam: Expand the monitor number of the resctrl root)
Signed-off-by: Zeng Heng <zengheng4@huawei.com>