sparc: Save/restore only non-volatile context

The _CPU_Context_switch() is a normal function call.  The following
registers are volatile (the caller must assume that the register
contents are destroyed by the callee) according to "SYSTEM V APPLICATION
BINARY INTERFACE - SPARC Processor Supplement", Third Edition: g1, o0,
o1, o2, o3, o4, o5.  Drop these registers from the context.

Ensure that offset defines match the structure offsets.
score: Change debug helper functions

Rename rtems_internal_error_description() to
rtems_internal_error_text().  Rename rtems_fatal_source_description() to
rtems_fatal_source_text().  Rename rtems_status_code_description() to
rtems_status_text().  Remove previous implementation of
rtems_status_text().
testsuites: Add TESTS_USE_PRINTF

Make it possible to use normal printf() if requested to allow output of
floating point numbers.