arc: Update ARC700 cache hazard detection.

arc: Update ARC700 cache hazard detection.

Replace/update ARC700 cache hazard detection. The next situations are
handled:

- There are 2 stores back2back, then 3 loads in next 3 or 4 instructions.

    if 3 loads in 3 instructions then we insert 2 nops after stores.
    if 3 loads in 4 instructions then we insert 1 nop after stores

- 2 back to back stores, followed by at least 3 loads in next 4 instructions.
        st st ld ld ld ##
        st st ## ld ld ld
        st st ld ## ld ld
        st st ld ld ## ld
        ## - any instruction

- store between non-store instructions, followed by 3 loads
        $$ st SS ld ld ld
        $$ - non-store instruction, even load.

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

	* config/arc/arc.c (arc_active_insn): Ignore all non essential
	instructions when getting the next active instruction.
	(check_store_cacheline_hazard): Update.
	(workaround_arc_anomaly): Remove obsolete cache hazard code.

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