PCI: add PCI Advanced Feature Capability defines

PCI Advanced Features Capability is introduced by "Conventional PCI
Advanced Caps ECN" (can be downloaded in pcisig.com).  Add defines for
the various AF capabilities, including function level reset (FLR).

Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Sheng Yang <sheng@linux.intel.com>
Signed-off-by: Jesse Barnes <jbarnes@virtuousgeek.org>