This patch adds handling of floating point instructions
fadd, fsub, fmul and fdiv. Regarding frem, Mips32 does not have
instruction that calculates partial reminder, so it has to be
emulated with a set of instructions. Emulating frem will be addressed
in separate patch, when floating point format conversion instructions
are fully implemented.

BUG=
R=stichnot@chromium.org

Review URL: https://codereview.chromium.org/2027773002 .

Patch from Srdjan Obucina <Srdjan.Obucina@imgtec.com>.