[SystemZ] Optimize 32-bit FPR<->GPR moves for z196 and above

Floats are stored in the high 32 bits of an FPR, and the only GPR<->FPR
transfers are full-register transfers.  This patch optimizes GPR<->FPR
float transfers when the high word of a GPR is directly accessible.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191764 91177308-0d34-0410-b5e6-96231b3b80d8
[SystemZ] Add test missing from r191764.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@191765 91177308-0d34-0410-b5e6-96231b3b80d8