arc: Refurbish adc/sbc patterns

arc: Refurbish adc/sbc patterns

The adc/sbc patterns were unecessary spliting, remove that and
associated functions.

gcc/
2020-12-11  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc-protos.h (arc_scheduling_not_expected): Remove
	it.
	(arc_sets_cc_p): Likewise.
	(arc_need_delay): Likewise.
	* config/arc/arc.c (arc_sets_cc_p): Likewise.
	(arc_need_delay): Likewise.
	(arc_scheduling_not_expected): Likewise.
	* config/arc/arc.md: Convert adc/sbc patterns to simple
	instruction definitions.

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