MFC 232362,232363,232463,232553,232569,232571:

• Sort function prototypes.
• Update the documentation on pci_get/set_powerstate(). These methods are not ACPI-specific at all, but deal with PCI power states. Also, pci_set_powerstate() fails with EOPNOTSUPP if a request is made that the underlying device does not support rather than falling back to somehow setting D0.
• Document the following routines: pci_alloc_msi(), pci_alloc_msix(), pci_find_cap(), pci_get_max_read_req(), pci_get_vpd_ident(), pci_get_vpd_readonly(), pci_msi_count(), pci_msix_count(), pci_pending_msix(), pci_release_msi(), pci_remap_msix(), and pci_set_max_read_req().
• Group the functions into five sub-sections: raw configuration access, locating devices, device information, device configuration, and message signaled interrupts.
• Discourage use of pci_disable_io() and pci_enable_io() in device drivers. The PCI bus driver handles this automatically as resources are activated.