This is another pass at making sure that nothing outside the BSP

unnecessarily uses any variables defined by the BSP.  On this
sweep, use of BSP_Configuration and Cpu_table was eliminated.

A significant part of this modification was the addition of
macros to access fields in the RTEMS configuration structures.

This is necessary to strengthen the division between the BSP independent
parts of RTEMS and the BSPs themselves.  This started after
comments and analysis by Ralf Corsepius <corsepiu@faw.uni-ulm.de>.

c/src/lib/libcpu/powerpc/shared/cpu.h

@@ -247,7 +247,7 @@ n:
   do { \
     unsigned32 start, ticks, now; \
     CPU_Get_timebase_low( start ) ; \
-    ticks = (_microseconds) * Cpu_table.clicks_per_usec; \
+    ticks = (_microseconds) * rtems_cpu_configuration_get_clicks_per_usec(); \
     do \
       CPU_Get_timebase_low( now ) ; \
     while (now - start < ticks); \