Enables vector division by scalarization.

Also, removed an assert as suggested by Karl in a previous CL:
https://codereview.chromium.org/1646033002/diff/1/src/IceInstARM32.cpp#newcode717

BUG= https://bugs.chromium.org/p/nativeclient/issues/detail?id=4076
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/1681003002 .