ada: Update Bit Ordering references in GNAT Reference Manual

ada: Update Bit Ordering references in GNAT Reference Manual

They are still tailored to Ada 95 while the level of recommended support for
Bit Ordering was changed in Ada 2005.

gcc/ada/

	* doc/gnat_rm/implementation_advice.rst (Representation Clauses):
	Remove >> marker and add end of sentence after code-block directive.
	(RM 13.5.3(7-8)): Update to Ada 2005 wording.
	* doc/gnat_rm/implementation_defined_characteristics.rst
	(RM 13.5.3(5)): Likewise.
	* gnat_rm.texi: Regenerate.
	* gnat_ugn.texi: Regenerate.