Implement _tsc_read equivalent for ARM

[zephyrbot]

Reported by Anas Nashif:

This is needed for benchmarks and boot time measurements

(Imported from Jira ZEP-1560)

[zephyrbot]

by Mark Linkmeyer:

Fixing incorrect priority

[zephyrbot]

by Mark Linkmeyer:

Maureen Helm , is this going to get done in 1.8? If so, please move it To Do status.

[zephyrbot]

by Mark Linkmeyer:

Maureen Helm , in cleaning up issues in preparation of the move to GitHub issues, I cleared the FixVersion field for this story because it was set to 1.8 and 1.8 was already released. If you know when it is now planned to be released, please set the FixVersion field accordingly.

[zephyrbot]

Blocks GH-2891