Add tickless kernel support in xtensa_sys_timer timer

[zephyrbot]

Reported by Ramesh Thomas:

Update the xtensa_sys_timer timer to support tickless kernel. It should interface with the tickless kernel APIs provided by the kernel and implement an event based management of time. It should also track time using wall time (MS or US) instead of ticks.

(Imported from Jira ZEP-1820)

[zephyrbot]

by Andrew Boie:

Upgrade to P2 and scope for 1.9. Good Xtensa support in Zephyr is a priority.

[zephyrbot]

by Mark Linkmeyer:

Youvedeep plans to talk to Anas (when Anas returns from vacation on the 24th) about potentially moving this to 1.10.

[zephyrbot]

by Andrew Boie:

Mark Linkmeyer I'm the one who set 1.9 for this ticket.
I have no problem pushing to 1.10.