PM / devfreq: Allow devfreq driver to add custom sysfs ABIs

Extend the devfreq_dev_profile to allow drivers optionally create
device-specific sysfs ABIs together with other common devfreq ABIs under
the devfreq device path.

Reviewed-by: Jonathan Cameron <jonathan.cameron@huawei.com>
Reviewed-by: Huisong Li <lihuisong@huawei.com>
Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>
Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Link: https://patchwork.kernel.org/project/linux-pm/patch/20250623143401.4095045-2-zhanjie9@hisilicon.com/