Bare metal: Enable signals greentea test

[rajkan01]

Summary of changes

The signals greentea test was disabled in bare metal profile as initially, Mbed OS did not have signals implementation without using RTOS APIs, but recently support added. So enabled all the test cases except thread-based one, added the new test cases based on ticker instead of thread.

Impact of changes

With these changes, the baremetal signals greentea test successfully builds and run.

Migration actions required

None.

Documentation

None.

---

Pull request type

[x] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[] Feature update (New feature / Functionality change / New API)
[] Major update (Breaking change E.g. Return code change / API behaviour change)

---

Test results

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[] Tests / results supplied as part of this PR

---

Reviewers

@evedon @kjbracey-arm

---

[kjbracey]

Looks fine to me, but will cause conflict with #12425 yet again. (Each time one of these gets merged, I have to Chrono-ify it in that PR).

[0xc0170]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 4 of 4 test jobs passed
Build number : 1
Build artifacts