To support runtime PM, use the function 'pci_set_power_state' to change
the power state. Therefore, method _PS0 or _PR0 needs to be filled by
platform. So check whether the method is supported, if not, print a
prompt information.
Signed-off-by: Weili Qian <qianweili@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>