Make STM32F412xE targets build

[mikrodust-henrikp]

Summary of changes

Trying to inherit the STM32F412xE target makes the linker fail, since
CRASH_DATA_RAM_START is not present. Comparing LD scripts with the
STM32F412xG (which has active targets) it seems that the xE variant has
missed some updates somewhere. Since the LD scripts are otherwise
identical, copying the (working) ones from STM32F412xG seems to do the
trick.

Also added flash_data.h which was missing and needed here and there
(copied from xG and updated to fit the xE flash layout).

Impact of changes

Migration actions required

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)

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Test results

[x] 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]

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

[jeromecoutant]

2 comments before review:

• note that this crash data feature can be enabled in your local mbed_app.json file or in the the defualt configuration there:
  https://github.com/ARMmbed/mbed-os/blob/master/platform/mbed_lib.json#L241

• As files in TARGET_STM32F412xE are available, you could/should add the MCU_STM32F412xE support in targets.json like:
  https://github.com/ARMmbed/mbed-os/blob/master/targets/targets.json#L1917-L1932

[mikrodust-henrikp]

2 comments before review:

• note that this crash data feature can be enabled in your local mbed_app.json file or in the the defualt configuration there:
  https://github.com/ARMmbed/mbed-os/blob/master/platform/mbed_lib.json#L241
• As files in TARGET_STM32F412xE are available, you could/should add the MCU_STM32F412xE support in targets.json like:
  https://github.com/ARMmbed/mbed-os/blob/master/targets/targets.json#L1917-L1932

I've added the MCU_STM32F412xE in targets.json as well. As for the crash data feature that probably should be per board, so leaving that for later.

[0xc0170]

@jeromecoutant are you happy with the changes?

[jeromecoutant]

FYI: ARMmbed/stm32customtargets@8fb6269

[0xc0170]

Ci started

[mbed-ci]

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