arc: Update doloop_end patterns

arc: Update doloop_end patterns

ARC processor can use LP instruction to implement zero overlay loops.
The current inplementation doesn't handle the unlikely situation when
the loop iterator is located in memory.  Refurbish the loop_end insn
pattern into a define_insn_and_split pattern.

gcc/
2021-07-09  Claudiu Zissulescu  <claziss@synopsys.com>

	* config/arc/arc.md (loop_end): Change it to
	define_insn_and_split.

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