[arm] Improvements to negvsi4 and negvdi4.

[arm] Improvements to negvsi4 and negvdi4.

The generic expansion code for negv does not try the subv patterns,
but instead emits a sub and a compare separately.  Fortunately, the
patterns can make use of the new subv operations, so just call those.
We can also rewrite this using an iterator to simplify things further.
Finally, we can now make negvdi4 work on Thumb2 as well as Arm.

	* config/arm/arm.md (negv<SIDI:mode>3): New expansion rule.
	(negvsi3, negvdi3): Delete.
	(negdi2_compare): Delete.

From-SVN: r277191