Fix alignment problem with some 64bit load/store instructions

LD/STD/LWA require displacement to be multiple of 4, provide
tcg_out_ldsta which checks the supplied displacement and falls
back on indexed variant when the check fails. All uses of
LD/STD/LWA outside of tcg_out_ldst appear to be safe.

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5670 c046a42c-6fe2-441c-8c8c-71466251a162
