ARM: Mark VSELECT as 'expand'.

The backend already pattern matches to form VBSL when it can. We may want to
teach it to use the vbsl intrinsics at some point to prevent machine licm from
mucking with this, but using the Expand is completely correct.

http://llvm.org/bugs/show_bug.cgi?id=13831
http://llvm.org/bugs/show_bug.cgi?id=13961

Patch by Peter Couperus <peter.couperus@st.com>.

llvm-svn: 165845