Optimize interrupt return code on ARC.

[zephyrbot]

Reported by Benjamin Walsh:

There are too many pushes and pops on the stack when deciding which thread to run when exiting an interrupt. Also, see if _is_next_thread_current and _get_next_ready_thread could not be folded together. Or maybe write _is_next_thread_current in assembly.

(Imported from Jira ZEP-1230)

[zephyrbot]

by Deli Niu:

From the view of PnP, it could be verified by latency benchmark.

1. On quark_se_c1000_devboard, run benchmark in folder /tests/legecy/benchmark/latency_measure/
2. Get the latency time of switching ISR back to interrupted task.

New:
Measure time to switch from ISR back to interrupted task switching time is 259 tcs = 8093 nsec

Old:
Measure time to switch from ISR back to interrupted task switching time is 269 tcs = 8406 nsec

[zephyrbot]

by Mark Linkmeyer:

Fixing incorrect priority