[Mips] Adjust float ABI settings in case of MIPS16 mode.

Hard float for mips16 means essentially to compile as soft float but to
use a runtime library for soft float that is written with native mips32
floating point instructions (those runtime routines run in mips32 hard
float mode).

The patch reviewed by Reed Kotler.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@195123 91177308-0d34-0410-b5e6-96231b3b80d8