CONFIG_ARM64_AMU_EXTN is not available for the default architecture x86.
Result is shown for architecture arm64

Enable support for the Activity Monitors Unit CPU extension

configname: CONFIG_ARM64_AMU_EXTN

Linux Kernel Configuration
└─> Kernel Features
└─> ARMv8.4 architectural features
└─> Enable support for the Activity Monitors Unit CPU extension

The activity monitors extension is an optional extension introduced
by the ARMv8.4 CPU architecture. This enables support for version 1
of the activity monitors architecture, AMUv1.

To enable the use of this extension on CPUs that implement it, say Y.

Note that for architectural reasons, firmware _must_ implement AMU
support when running on CPUs that present the activity monitors
extension. The required support is present in:
* Version 1.5 and later of the ARM Trusted Firmware

For kernels that have this configuration enabled but boot with broken
firmware, you may need to say N here until the firmware is fixed.
Otherwise you may experience firmware panics or lockups when
accessing the counter registers. Even if you are not observing these
symptoms, the values returned by the register reads might not
correctly reflect reality. Most commonly, the value read will be 0,
indicating that the counter is not enabled.