Check for the "rtems/pci.h" header and provide conditional build support
with waf to build for BSPs that do not have PCI support. The Makefile build
always defines HAVE_RTEMS_PCI_H which is the same state with this change.
The PCI calls still exist however they do nothing and return a constant.
Any PCI based driver that makes these calls on a BSP that does not have
PCI support will not work which is understandable. Either change the
driver or add PCI support the BSP.
