target/mips: Convert Vr54xx MSA* opcodes to decodetree

target/mips: Convert Vr54xx MSA* opcodes to decodetree

Convert the following Integer Multiply-Accumulate opcodes:

 * MSAC         Multiply, negate, accumulate, and move LO
 * MSACHI       Multiply, negate, accumulate, and move HI
 * MSACHIU      Unsigned multiply, negate, accumulate, and move HI
 * MSACU        Unsigned multiply, negate, accumulate, and move LO

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20210808173018.90960-8-f4bug@amsat.org>