[MIPS] Use hard float calling convention for managed code

Note that this isn't o32 ABI. Same set of registers is used for
arguments ($a0-$a3 and $f12-$f15), but we don't skip registers
and fp arguments are never passed via core registers.

Change-Id: Ifb883ff6e15758b539137898b49ac2f8ee075f49
13 files changed