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/support/include/test_support.h

@@ -74,8 +74,6 @@ int locked_printf(const char *fmt, ...);
 
 int locked_vprintf(const char *fmt, va_list ap);
 
-int locked_printf_plugin(void *context, const char *fmt, ...);
-
 void locked_printk(const char *fmt, ...);
 
 #ifdef __cplusplus