_targets: configure building coremark port

[lukileczo]

JIRA: RTOS-832

Description

Add coremark port.

Motivation and Context

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[nalajcie]

I don't think enabling new ports by default in target files is the way to go (eg. right now You've added new binary in DTR project making rootfs/update pkg bigger than before - I think this was not intended?).

Maybe we should enable working ports in our reference projects (so in _project subdir?)