target/sh4: Rename TCGv variables as manual for SUBV opcode

To easily compare with the SH4 manual, rename:

  REG(B11_8) -> Rn
  REG(B7_4) -> Rm
  t0 -> result

Mention how underflow is calculated.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20240430163125.77430-5-philmd@linaro.org>
1 file changed