[arm] Improve code generation for addvsi4.

[arm] Improve code generation for addvsi4.

Similar to the improvements for uaddvsi4, this patch improves the code
generation for addvsi4 to handle immediates and to add alternatives
that better target thumb2.  To do this we separate out the expansion
of uaddvsi4 from that of uaddvdi4 and then add an additional pattern
to handle constants.  Also, while doing this I've fixed the incorrect
usage of NE instead of COMPARE in the generated RTL.

	* config/arm/arm.md (addv<mode>4): Delete.
	(addvsi4): New pattern.  Handle immediate values that the architecture
	supports.
	(addvdi4): New pattern.
	(addsi3_compareV): Rename to ...
	(addsi3_compareV_reg): ... this.  Add constraints for thumb2 variants
	and use COMPARE rather than NE.
	(addsi3_compareV_imm): New pattern.
	* config/arm/arm.c (arm_select_cc_mode): Return CC_Vmode for
	a signed-overflow check.

From-SVN: r277184