ARM: Mark double-precision instructions as such

This prevents us from silently accepting invalid instructions on (for example)
Cortex-M4 with just single-precision VFP support.

No tests for the extra Pat Requires because they're essentially assertions: the
affected code should have been lowered to libcalls before ISel.

rdar://problem/15302004

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193354 91177308-0d34-0410-b5e6-96231b3b80d8