cpukit, testsuite: Add rtems_printf and rtems_printer support.

This change adds rtems_printf and related functions and wraps the
RTEMS print plugin support into a user API. All references to the
plugin are removed and replaced with the rtems_printer interface.

Printk and related functions are made to return a valid number of
characters formatted and output.

The function attribute to check printf functions has been added
to rtems_printf and printk. No changes to remove warrnings are part
of this patch set.

The testsuite has been moved over to the rtems_printer. The testsuite
has a mix of rtems_printer access and direct print control via the
tmacros.h header file. The support for begink/endk has been removed
as it served no purpose and only confused the code base. The testsuite
has not been refactored to use rtems_printf. This is future work.

testsuites/libtests/stackchk/system.h

@@ -11,6 +11,7 @@
  *  http://www.rtems.org/license/LICENSE.
  */
 
+#define TESTS_USE_PRINTK
 #include <tmacros.h>
 
 /* macros */