x86/resctrl: Describe resctrl's bitmap size assumptions

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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resctrl stores the bitmaps and has a closid bitmap stored in u32.

MPAM supports bitmaps and partids bigger than this.

Add some preprocessor values that make it clear why MPAM clamps
some of these values.

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