x86/PCI: VMD: Request userspace control of PCIe hotplug indicators

Add set_dev_domain_options() to set PCI domain-specific options as devices
are added.  The first usage is to request exclusive userspace control of
PCIe hotplug indicators in VMD domains.

Devices in a VMD domain use PCIe hotplug Attention and Power Indicators in
a non-standard way; tell pciehp to ignore the indicators so userspace can
control them via the sysfs "attention" file.

To determine whether a bus is within a VMD domain, add a bool to the
pci_sysdata structure that the VMD driver sets during initialization.

[bhelgaas: changelog]
Requested-by: Kapil Karkra <kapil.karkra@intel.com>
Tested-by: Artur Paszkiewicz <artur.paszkiewicz@intel.com>
Signed-off-by: Keith Busch <keith.busch@intel.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>