LoongArch: Add acpi_get_cpu_uid() for unified ACPI CPU UID retrieval

LoongArch: Add acpi_get_cpu_uid() for unified ACPI CPU UID retrieval

As a step towards unifying the interface for retrieving ACPI CPU UID
across architectures, introduce a new function acpi_get_cpu_uid() for
loongarch. While at it, add input validation to make the code more
robust.

Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20260401081640.26875-3-fengchengwen@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>