Handle register copies for the new ARM register classes.

ARM recently gained DPair, DTriple, and DQuad register classes.
Update copyPhysReg() to handle copies in these register classes.

No test case, it is difficult to make the register allocator emit the
odd copies reliably. The missing DPair copy caused a failure on
partialsums in the nightly test suite.

<rdar://problem/11147997>

llvm-svn: 153686