Rename loongarch-fpu64.xml to loongarch-fpu.xml and update
loongarch-fpu.xml to match upstream GDB [1]

[1]:https://github.com/bminor/binutils-gdb/blob/master/gdb/features/loongarch/fpu.xml



Signed-off-by: Song Gao <gaosong@loongson.cn>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Acked-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20220805033523.1416837-5-gaosong@loongson.cn>