MIPS: math-emu: Add support for the MIPS R6 RINT FPU instruction

MIPS R6 introduced the following instruction:
Floating-Point Round to Integral
Scalar floating-point round to integral floating point value.

RINT.fmt: FPR[fd] = round_int(FPR[fs])

Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/10958/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>