score: Scheduler documentation
score: Introduce scheduler nodes

Rename scheduler per-thread information into scheduler nodes using
Scheduler_Node as the base type.  Use inheritance for specialized
schedulers.

Move the scheduler specific states from the thread control block into
the scheduler node structure.

Validate the SMP scheduler node state transitions in case RTEMS_DEBUG is
defined.
score: SMP scheduler documentation
score: Capitalize SMP acronym
score: Use Scheduler_Context for SMP scheduler

Use the basic Scheduler_Context for the general SMP scheduler operations
to avoid usage of structure offsets to get the specialized context
variants.
bsps/sparc: Fix data copy in start procedure

Use the register %g4 for the data content since it must be an even
numbered register due to the std/ldd.  Use the register %g2 for the BSS
start address, so that it can be later re-used for the BSS zero loop.
bsps/sparc: Fix BSS initialization

Use __bss_start available via %g2 to clear the BSS section.  The usage
of _edata resulted in a copy of [_edata, __bss_start) from ROM to RAM
and then a clear to zero of this area.

Clear now only [__bss_start, _end).