Allow ThreadInterface::device_eui64_get() before connect()

[kjbracey]

Description

Perform necessary driver initialisation so that we can read the EUI-64 before connecting.

Fixes #7391.

Pull request type

[ ] Fix
[X] Refactor
[ ] Target update
[ ] Functionality change
[ ] Breaking change

Marked as refactor as it's a non-trivial initialisation rework, and it wasn't necessarily intended to permit this ordering originally, although it makes sense.

[0xc0170]

/morph build

[mbed-ci]

Build : SUCCESS

Build number : 2909
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/7818/

Triggering tests

/morph test
/morph uvisor-test
/morph export-build
/morph mbed2-build

[mbed-ci]

Test : SUCCESS

Build number : 2659
Test logs :http://mbed-os-logs.s3-website-us-west-1.amazonaws.com/?prefix=logs/7818/2659

[mbed-ci]

Exporter Build : SUCCESS

Build number : 2531
Build artifacts/logs : http://mbed-os.s3-website-eu-west-1.amazonaws.com/?prefix=builds/exporter/7818/

[cmonr]

/morph uvisor-test

[cmonr]

@ARMmbed/mbed-os-maintainers Since uVisor is being removed in 5.10, and this PR is only targeting 5.10, anyone object to bringing it in even though the PR is not all green?

I've already removed uVisor as a branch chcek, but if the test ran in a PR before it was removed, it'll still show up in the check list.

[0xc0170]

I've already removed uVisor as a branch chcek, but if the test ran in a PR before it was removed, it'll still show up in the check list.

We need to remove uvisor trigger from build comment (manual driver if needed for now). And this check, will be fixed.

[cmonr]

@SeppoTakalo @KariHaapalehto Would y'all mind taking a look at this? It's ready for merge otherwise.