target/mips: Convert Vr54xx MUL* opcodes to decodetree

target/mips: Convert Vr54xx MUL* opcodes to decodetree

Convert the following Integer Multiply-Accumulate opcodes:

 * MULHI        Multiply and move HI
 * MULHIU       Unsigned multiply and move HI
 * MULS         Multiply, negate, and move LO
 * MULSHI       Multiply, negate, and move HI
 * MULSHIU      Unsigned multiply, negate, and move HI
 * MULSU        Unsigned multiply, negate, and move LO

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210808173018.90960-7-f4bug@amsat.org>