STM32 baremetal support step3/3 (F2/F4)

[jeromecoutant]

Summary of changes

Major patches are linker script updates to support baremetal.
This follows #12992 and #13001

@MarceloSalazar @evedon
@ARMmbed/team-st-mcd

Impact of changes

Migration actions required

Documentation

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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)

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Test results

Baremetal tests are OK:
mbed test xxx --test-config tests/configs/baremetal.json

[] 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

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Reviewers

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[ciarmcom]

@jeromecoutant, thank you for your changes.
@ARMmbed/mbed-os-maintainers please review.

[adbridge]

CI started

[mbed-ci]

Test run: SUCCESS

Summary: 7 of 7 test jobs passed
Build number : 1
Build artifacts