target/loongarch: Add floating point arithmetic instruction translation

This includes:
- F{ADD/SUB/MUL/DIV}.{S/D}
- F{MADD/MSUB/NMADD/NMSUB}.{S/D}
- F{MAX/MIN}.{S/D}
- F{MAXA/MINA}.{S/D}
- F{ABS/NEG}.{S/D}
- F{SQRT/RECIP/RSQRT}.{S/D}
- F{SCALEB/LOGB/COPYSIGN}.{S/D}
- FCLASS.{S/D}

Signed-off-by: Song Gao <gaosong@loongson.cn>
Signed-off-by: Xiaojuan Yang <yangxiaojuan@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220606124333.2060567-11-yangxiaojuan@loongson.cn>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>