Introduced FSELECT node necesary when lowering ISD::SELECT which
has i32, f64, f64 as its operands.
SEL_D instruction required that its output and first operand of
SELECT node, which it used, have matching types.
MTC1_D64 node introduced to aid FSELECT lowering.
This fixes machine verifier errors on following files:
CodeGen/Mips/llvm-ir/select-dbl.ll
CodeGen/Mips/llvm-ir/select-flt.ll
CodeGen/Mips/select.ll