Add power management block device driver for changing the power mode of Flash

[rogeryou]

Summary of changes

Usually, Nor Flash has more than one power mode, such as high performance mode, low power mode and deep down mode. But in QSPIF block device driver, it is not very easy to change Flash power mode. The PowerManagementBlockDevice class provides an API to change the Flash power mode if the underlying block device doesn’t support such a behavior, which is only support the MX25R6435F of QSPIF block device temporarily. But，users can add codes for other power modes of other types of Flash.

Impact of changes

Migration actions required

Documentation

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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)
[x] Tests / results supplied as part of this PR

mbedgt: test suite report:

target	platform_name	test suite	result	elapsed_time (sec)	copy_method
DISCO_L475VG_IOT01A-GCC_ARM	DISCO_L475VG_IOT01A	storage-blockdevice-tests-tests-blockdevice-power_management_block_device	OK	9.71	default
mbedgt: test suite results: 1 OK

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Reviewers

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[ciarmcom]

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

[0xc0170]

Similar to the PR #15242 ,what shall we do with this PR?