Add lbarx/stbcx., lharx/sthcx. and lqarx/stqcx. single stepping

Newer CPUs support byte, half word and quad word atomic update
sequences.

gdb/testsuite/
2014-03-28  Anton Blanchard  <anton@samba.org>

	* rs6000-tdep.c (ppc_deal_with_atomic_sequence): Add single step
	support for lbarx/stbcx., lharx/sthcx. and lqarx/stqcx.