RFS: Use unprotected chain operations

This area is protected by the RFS file system instance lock.
libblock: Use unprotected chain extract

This area is protected by the media mutex.
bsps: Fix header includes
score: Add and use CHAIN_INITIALIZER_ONE_NODE().

Add and use CHAIN_NODE_INITIALIZER_ONE_NODE_CHAIN(),
RTEMS_CHAIN_INITIALIZER_ONE_NODE() and
RTEMS_CHAIN_NODE_INITIALIZER_ONE_NODE_CHAIN().
posix: Protect access to _POSIX_signals_Vectors

Assume the sigaction() is called only from thread context.  Protect
against concurrent sigaction() invocations by different threads.
Filesystem: Use unprotected chain operations

This area is protected by the IO library mutex.
ringbuf: Add SMP support
rtems: Add SMP support for signals

Add and use _ASR_Get_posted_signals().  The post-switch handler is not
protected by disabled thread dispatching.  Use proper SMP lock for
signal management.
posix: _POSIX_signals_Clear_process_signals()

Do not disable interrupts since the caller did this already.
sptests/spnsext01: Add SMP support
sptests/spthreadq01: Add SMP support
score: Add SMP support to _Watchdog_Report_chain()