tools: fix SPDX identifiers

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Co-Authored-By: theotherjimmy <theotherjimmy@gmail.com>

Apply suggestions from code review ...

Co-Authored-By: theotherjimmy <theotherjimmy@gmail.com>

Correct Python 3 errors and lint warnings in build_release.py ...

### Description

I think this file is still used, and it's about time we updated it for
compatibility with python3. While I was in there, I fixed all of the
linter warnings, so that it's easier to spot bad code.

### Pull request type

    [x] Fix
    [ ] Refactor
    [ ] Target update
    [ ] Functionality change
    [ ] Docs update
    [ ] Test update
    [ ] Breaking change

Add imports of basestring for python 3

Make release errors very visible

Correct status reporting of build_release.py

Use Notifier API when building mbed2

restructure - Updated tools to point to restructured modules ...

MBED_HAL       /hal/hal      x
MBED_API       /hal/api      x
MBED_COMMON    /hal/common   x
MBED_TARGETS   /hal/targets  ->  /targets
MBED_DRIVERS                  +  /drivers
MBED_PLATFORM                 +  /platform
MBED_HEADER                   +  /mbed.h

Adding build profiles configuration to build_release.py and singletest.py

Adding concept of release versions for targets. ...

Previously, the condition for including a target in a release was decided
by a 'release' key being set to 'true' in hal/targets.json. This doesn't
have enough granularity when we release multiple versions of mbed. This PR
changes the 'release' key to an array of strings, where each member is a
version that the target supports. Currently the valid versions are '2' and
'5'.

This PR also adds more robust checking for invalid target configurations
in a release. This is enforced whenever the release list is built from the
data, preventing invalid targets from coming into the release.

Finally, it updates the build_release.py script to use the new api for
fetching release targets.

Build release - add copy targets.json file

Build release - use target.release to produce release tuple

[STM32F4xx] Add support for NUCLEO_F429ZI

[NUCLEO_F446ZE] Add to build and export scripts

[NUCLEO_F7xx] adding F767 to build_release and adding default_build to target.json

[NUCLEO_L432KC] Add to build and export scripts

Merge pull request #1752 from svastm/add_nucleo_l011k4 ...

Add NUCLEO_L011K4

[BEETLE] Add initial support ...

This patch adds support for the BEETLE Target. The compilers supported by
this target are:
* ARMCC
* GCC ARM

The exporters and the CMSIS/HAL components will follow in future patches.

Signed-off-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

[NUCLEO_L011K4] Add to the build and export scripts

Renamed workspace_tools folder to tools