TF-M v1.2 support

[LDong-Arm]

As TF-M v1.2 support has been merged to Mbed OS, this PR brings in all the update we have made to support the regression tests and PSA compliance tests:

• Scripts updated to work with TF-M v1.2 (build commands, copying of TF-M build outputs, etc.)
• Greentea test support: test-spec generation, synchronisation, updated logs for comparison
• Support for nightly CI to rebase and build TF-M's master branch
• Documentation updated with the latest info
• Vagrant updated with the require packages and to provide a build environment only
• Clean-up: old libraries, files for the Cypress target (which doesn't support TF-M v1.2 yet), etc.
• General code-quality improvements: see the commit history

[LDong-Arm]

I accidentally cancelled "Travis CI - Branch" (regular run on each branch), but it's the same as "Travis CI - Pull Request" which is running, so it should be fine.

[evedon]

I accidentally cancelled "Travis CI - Branch" (regular run on each branch), but it's the same as "Travis CI - Pull Request" which is running, so it should be fine.

OK