Add conditional support for RTEMS PCI to the waf build.

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.

waf_generator.py

@@ -242,6 +242,7 @@ class ModuleManager(builder.ModuleManager):
         self.add('')
         self.add('def bsp_configure(conf, arch_bsp):')
         self.add('    conf.check(header_name = "dlfcn.h", features = "c")')
+        self.add('    conf.check(header_name = "rtems/pci.h", features = "c", mandatory = False)')
         self.add('')
         self.add('def configure(conf):')
         self.add('    if conf.options.auto_regen:')