Adapt tickless idle for x86

[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-910)

[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

quark_se LOAPIC timer: PASSED

quark_d2000 MVIC timer: PASSED

qemu_x86 HPET timer: generally working, bug have minor issues logged as GH-2573, GH-2574

Closing this. Thanks Peter Mitsis !