config: Add <rtems/confdefs/obsolete.h>

Unify handling of obsolete configuration options.  Remove comments and
copyrightable content from the moved content.  Use BSD-2-Clause license
for new file.

Update #3053.
Update #3875.

cpukit/header-dirs.am

@@ -50,6 +50,8 @@ include_rtems_bfindir = $(includedir)/rtems/bfin
 include_rtems_bfin_HEADERS =
 include_rtems_bsdnetdir = $(includedir)/rtems/bsdnet
 include_rtems_bsdnet_HEADERS =
+include_rtems_confdefsdir = $(includedir)/rtems/confdefs
+include_rtems_confdefs_HEADERS =
 include_rtems_debuggerdir = $(includedir)/rtems/debugger
 include_rtems_debugger_HEADERS =
 include_rtems_m68kdir = $(includedir)/rtems/m68k

cpukit/headers.am

@@ -183,6 +183,7 @@ include_rtems_HEADERS += include/rtems/userenv.h
 include_rtems_HEADERS += include/rtems/version.h
 include_rtems_HEADERS += include/rtems/vmeintr.h
 include_rtems_HEADERS += include/rtems/watchdogdrv.h
+include_rtems_confdefs_HEADERS += include/rtems/confdefs/obsolete.h
 include_rtems_debugger_HEADERS += include/rtems/debugger/rtems-debugger-bsp.h
 include_rtems_debugger_HEADERS += include/rtems/debugger/rtems-debugger-remote.h
 include_rtems_debugger_HEADERS += include/rtems/debugger/rtems-debugger-server.h