Add extern "C" around am_hal_secure_ota.h functions

[UbiJCC]

Summary of changes

Added extern "C" around functions in am_hal_secure_ota.h.

This change is necessary to use the Apollo3's Secure OTA functionality within mbed.

Fixes #14389

Impact of changes

Users may now call the functions declared in am_hal_secure_ota.h where they could not before.

Migration actions required

None

Documentation

None

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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

[X] No Tests required for this change (E.g docs only update)
[] 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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[0xc0170]

Is this just one header (the rest of files in hal/ are ok?)

[0xc0170]

Is this just one header (the rest of files in hal/ are ok?)

I've checked few other files under hal directory, they look good.

[UbiJCC]

Is this just one header (the rest of files in hal/ are ok?)

I have checked every header file under the TARGET_APOLLO3/sdk/mcu/apollo3/hal/ directory and can confirm this is the only header file (which declares any functions) missing the extern "C" declaration.

The only concern I have is that these files may be taken directly from AmbiqSuite SDK, and this change may (further?) diverge us, but frankly it seems this is an oversight in Ambiq's HAL in the first place.

[0xc0170]

CI started

[mbed-ci]

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