arc: Update (u)maddhisi4 patterns

arc: Update (u)maddhisi4 patterns

The (u)maddsihi4 patterns are using the ARC's VMAC2H(U)
instruction with null destination, however, VMAC2H(U) doesn't
rewrite the accumulator.  This patch solves the destination issue
of VMAC2H by replacing it with DMACH(U) instruction.

gcc/

	* config/arc/arc.md (maddhisi4): Use a single move to accumulator.
	(umaddhisi4): Likewise.
	(machi): Update pattern.
	(umachi): Likewise.

gcc/testsuite/

	* gcc.target/arc/tmac-4.c: New test.

Signed-off-by: Claudiu Zissulescu <claziss@synopsys.com>