rtems: Add rtems_scheduler_get_processor_maximum()

Add rtems_scheduler_get_processor_maximum() as a replacement for
rtems_get_processor_count(). The rtems_get_processor_count() is a bit
orphaned. Adopt it by the Scheduler Manager. The count is also
misleading, since the processor set may have gaps and the actual count
of online processors may be less than the value returned by
rtems_get_processor_count().

Update #3732.

testsuites/smptests/smpopenmp01/init.c

@@ -239,7 +239,7 @@ static uint32_t find_free_cpu(test_context *ctx)
   uint32_t i;
   uint32_t n;
 
-  n = rtems_get_processor_count();
+  n = rtems_scheduler_get_processor_maximum();
 
   pthread_mutex_lock(&ctx->mtx);