ACPI: CPPC: Add cppc_set_reg_val()

ACPI: CPPC: Add cppc_set_reg_val()

Add cppc_set_reg_val() as a generic function for setting CPPC register
values, with this features:

 1. Check register. If a register is writeable, it must be a buffer and
    can not be null.

 2. Extract the operations if register is in PCC out as
    cppc_set_reg_val_in_pcc().

This function can be used to reduce some existing code duplication.

Reviewed-by: Pierre Gondois <pierre.gondois@arm.com>
Signed-off-by: Lifeng Zheng <zhenglifeng1@huawei.com>
Reviewed-by: Mario Limonciello <mario.limonciello@amd.com>
Link: https://patch.msgid.link/20250411093855.982491-6-zhenglifeng1@huawei.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>