arm64/mpam: resctrl: Remove unnecessary CONFIG_ARM64

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

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Code in resctrlfs.c is not shared with x86 RDT currently, but may be
updated to support both in the future, so remove unrelated CONFIG for
now to make code clearer.

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>