[mips] Increase the number of floating point control registers available to 32.

Create a dedicated register class for floating point condition code registers and
move FCC0 from register class CCR to the new register class.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@185373 91177308-0d34-0410-b5e6-96231b3b80d8