[ARM] Cleanup highpart multiply patterns

[ARM] Cleanup highpart multiply patterns

Cleanup the various highpart multiply patterns using iterators.
As a result the signed and unsigned variants and the pre-Armv6
multiply operand constraints are all handled in a single pattern
and simple expander.

    gcc/
	* config/arm/arm.md (smulsi3_highpart): Use <US> and <SE> iterators.
	(smulsi3_highpart_nov6): Remove pattern.
	(smulsi3_highpart_v6): Likewise.
	(umulsi3_highpart): Likewise.
	(umulsi3_highpart_nov6): Likewise.
	(umulsi3_highpart_v6): Likewise.
	(<US>mull_high): Add new combined multiply pattern.

From-SVN: r275899