target/sparc: Remove DisasCompare.is_bool

Since we're going to feed cpu_cond to another comparison, we don't
reqire a boolean value -- anything non-zero is sufficient.

Tested-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Acked-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>