target/sparc: Check for invalid cond in gen_compare_reg

Consolidate the test here; drop the "inverted logic".
Fix MOVr and FMOVR, which were missing the invalid test.

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>