target/mips: Convert Loongson DIV.G opcodes to decodetree

target/mips: Convert Loongson DIV.G opcodes to decodetree

DIV.G and DDIV.G are very similar. Provide gen_lext_DIV_G() a
'is_double' argument so it can generate DIV.G (divide 32-bit
signed integers).

With this commit we explicit the template used to generate
opcode for 32/64-bit word variants. Next commits will be less
verbose by providing both variants at once.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20241026175349.84523-6-philmd@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>