Portenta H7: Add API to manage low power mode of CYW43xxx bluetooth chip

[leonardocavagnis]

Summary of changes

Adding API to manage low power mode of CYW43xxx bluetooth chip in Portenta H7 board. Low power mode is enabled by default and the status can be changed with a dedicated function.

Impact of changes

Migration actions required

Documentation

None

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Pull request type

[] Patch update (Bug fix / Target update / Docs update / Test update / Refactor)
[X] 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

[] 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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