[ARC] Update movhi and movdi patterns.

[ARC] Update movhi and movdi patterns.

Allow signed 6-bit short immediates into st[d] instructions.

2017-10-19  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.c (arc_split_move): Allow signed 6-bit constants
	as source of std instructions.
	* config/arc/arc.md (movsi_insn): Update pattern predicate to
	allow 6-bit constants as source for store instructions.
	(movdi_insn): Update instruction pattern to allow 6-bit constants
	as source for store instructions.

testsuite/
2017-10-19  Claudiu Zissulescu  <claziss@synopsys.com>

	* gcc.target/arc/store-merge-1.c: New test.
	* gcc.target/arc/add_n-combine.c: Update test.

From-SVN: r259762