target/ppc: Move neg, darn, mod{sw, uw} to decodetree.

target/ppc: Move neg, darn, mod{sw, uw} to decodetree.

Moving the below instructions to decodetree specification :

	neg[o][.]       	: XO-form
	mod{sw, uw}, darn	: X-form

The changes were verified by validating that the tcg ops generated by those
instructions remain the same, which were captured with the '-d in_asm,op' flag.

Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Chinmay Rath <rathc@linux.ibm.com>
[np: 32-bit compile fix]
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>