rename SelectScalarSSELoad -> SelectScalarSSELoadXXX and rewrite

rename SelectScalarSSELoad -> SelectScalarSSELoadXXX and rewrite
it to follow the mode needed by the new isel.  Instead of returning
the input and output chains, it just returns the (currently only one,
which is a silly limitation) node that has input and output chains.

Since we want the old thing to still work, add a new
SelectScalarSSELoad to emulate the old interface.  The XXX suffix
and the wrapper will eventually go away.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96715 91177308-0d34-0410-b5e6-96231b3b80d8