arm64 generates asm/pci-bridge.h, which merely includes the now-empty
asm-generic/pci-bridge.h.  Stop generating asm/pci-bridge.h, and stop
including it.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>
Acked-by: NWill Deacon <will.deacon@arm.com>