config: enable CONFIG_ARM64_AMU_EXTN to be compatible with AMU platform

hulk inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I73EPL



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The KunPeng newest released platform supports the feature of AMU,
and this configuration is backward compatible. This patch would
acts as a prepatch for the following patch series.

Signed-off-by: Zeng Heng <zengheng4@huawei.com>