xen-platform: Convert to generic power management

Convert xen-platform from the legacy PCI power management callbacks to the
generic operations.  This is one step towards removing support for the
legacy PCI callbacks.

The generic .resume_noirq() operation is called by pci_pm_resume_noirq() at
the same point the legacy PCI .resume_early() callback was, so this patch
should not change the xen-platform behavior.

Link: https://lore.kernel.org/r/20191101204558.210235-5-helgaas@kernel.org


Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: KarimAllah Ahmed <karahmed@amazon.de>