ACPI: CPPC: Move reference performance to capabilities

ACPI: CPPC: Move reference performance to capabilities

Currently, the `Reference Performance` register is read every time
the CPU frequency is sampled in `cppc_get_perf_ctrs()`. This function
is on the hot path of the cppc_cpufreq driver.

Reference Performance indicates the performance level that corresponds
to the Reference Counter incrementing and is not expected to change
dynamically during runtime (unlike the Delivered and Reference counters).

Reading this register in the hot path incurs unnecessary overhead,
particularly on platforms where CPC registers are located in the PCC
(Platform Communication Channel) subspace. This patch moves
`reference_perf` from the dynamic feedback counters structure
(`cppc_perf_fb_ctrs`) to the static capabilities structure
(`cppc_perf_caps`).

Signed-off-by: Pengjie Zhang <zhangpengjie2@huawei.com>
[ rjw: Changelog adjustment ]
Link: https://patch.msgid.link/20260213100935.19111-1-zhangpengjie2@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>