Adapt tickless idle + power management for ARM

[zephyrbot]

Reported by Benjamin Walsh:

Adapt _sys_power_save_idle() and _sys_power_save_idle_exit() for unified kernel.
Adapt power management hooks. Make sure unified kernel invokes them.

Done criteria:

Unified kernel APIs are operational. Underlying code follows the revised kernel naming conventions.
Legacy APIs are operational.

(Imported from Jira ZEP-909)

[zephyrbot]

by Peter Mitsis:

Tickless idle support in the unified kernel was added in commit 96cb05c.

[zephyrbot]

by Sharron LIU:

testpoints:

TESTPOINT: verify the "programmed cycles". Expect the error cycles are within one tick (CYCLES_PER_TICK). NOTE, this is expected regardless straddled tick boundary or not.
TESTPOINT: verify system clock after exiting tickless idle. Expect system clock recovered with time elapsed during tickless idle

2 test cases covering above test points

arduino_due COTEXT_M_SYSTICK timer

For the 1st test point, I observed minor issue logged as GH-2575. I would need your confirmation that such behavior is as expected before I can close this story.
For the 2nd test point, PASSED. Thanks Peter Mitsis !

And, I also observed compilation failure in "kernel/unified/idle.c", logged as GH-2576.

[zephyrbot]

by Sharron LIU:

Closing this, and let the discussion followed by GH-2575 and GH-2576.