RISC-V: ACPI: Add acpi_get_cpu_uid() for unified ACPI CPU UID retrieval

RISC-V: ACPI: 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
riscv. While at it, add input validation to make the code more robust.

And also update acpi_numa.c and rhct.c to use the new interface instead
of the legacy get_acpi_id_for_cpu().

Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Link: https://patch.msgid.link/20260401081640.26875-4-fengchengwen@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>