[ARM] Mark VMOVDRR with the RegSequence property and implement the related
target hook.

This patch teaches the compiler that:
dX = VMOVDRR rY, rZ
is the same as:
dX = REG_SEQUENCE rY, ssub_0, rZ, ssub_1

<rdar://problem/12702965>


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215404 91177308-0d34-0410-b5e6-96231b3b80d8