usb/host: enable auto power control for xhci-pci

[why]
USB control should enter D3 state with no device connected

[How]
Enable runtime power management for XHCI-PCI USB host controller

Jira-ID: MR-1739/AER-588
Signed-off-by: Liang Liang (Leo) <liang.liang@amd.com>
Signed-off-by: Ziyang Wu <ziyang.wu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>