ACPI / PCI / PCIe: Rework _OSC handling (v3)

Hi,

This is the 3rd iteration of the patchset based on
https://patchwork.kernel.org/patch/114917/ and the comments I received on that patch and the previous two iterations of this patchset.

The patches below do not make the intermediate step to put an unconditional _OSC query into acpi_pci_osc_control_set(), but the final result is quite similar to the 2nd iteration with https://patchwork.kernel.org/patch/116976/
applied on top.

[1/10] - Introduce acpi_pci_osc_control_query() allowing the caller to get a
mask of _OSC control bits the BIOS allows the kernel to control for a given PCI root bridge. This version repeats _OSC queries until the BIOS doesn't mask any requested bits.

[2/10] - Introduce pci_aer_available() allowing the caller to check if the
AER service driver should be enabled.

[3/10] - Introduce kernel command line switch pcie_ports=.

[4/10] - Rework the PCIe port driver to request _OSC control for all serives at
once.

[5/10] - Disable PCIe port services (that might be enabled by the BIOS) during
initialization.

[6/10] - Remove the PCIe port driver modules exit function.

[7/10] - Make PCI hotplug code query _OSC before requesting control of _OSC
features.

[8/10] - Rework acpi_pci_osc_control_set() so that it doesn't use cached
result of a query and remove the fields of struct acpi_pci_root that aren't used any more.

[9/10] - Reorder checks in acpi_pci_osc_control_set().

[10/10] - Merge acpi_pci_osc_control_set() with acpi_pci_osc_control_query().

Comments welcome.

Thanks,
Rafael