arc: Improve/add instruction patterns to better use MAC instructions.

arc: Improve/add instruction patterns to better use MAC instructions.

ARC MYP7+ instructions adds MAC instructions for either vector and
scalar data types. This patch adds a madd pattern for 16it datum using
the 32bit MAC instruction, and dot_prod patterns for v4hi vector
types. The 64bit moves are also upgraded by using vadd2 instuction.

2020-11-09  Claudiu Zissulescu  <claziss@synopsys.com>

gcc/

	* config/arc/arc.c (arc_split_move): Recognize vadd2 instructions.
	* config/arc/arc.md (movdi_insn): Update pattern to use vadd2
	instructions.
	(movdf_insn): Likewise.
	(maddhisi4): New pattern.
	(umaddhisi4): Likewise.
	* config/arc/simdext.md (mov<mode>_int): Update pattern to use
	vadd2.
	(sdot_prodv4hi): New pattern.
	(udot_prodv4hi): Likewise.
	(arc_vec_<V_US>mac_hi_v4hi): Update/renamed to
	arc_vec_<V_US>mac_v2hiv2si.
	(arc_vec_<V_US>mac_v2hiv2si_zero): New pattern.
	* config/arc/constraints.md (Ral): Accumulator register
	constraint.

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