Fix duplication of KW41Z Nanostack driver

[LDong-Arm]

Summary of changes

In #13119 we moved Nanostack target drivers into nanostack-interface/targets, to fix issues with bare-metal (i.e. no mbed_lib.json to guard unused libraries). But at roughly the same time, #13115 (rename TARGET_NXP to TARGET_Freescale) was made in the old path. Now we end up with identical KW41Z drivers in two different places.

This PR resolves the issue:

• driver under nanostack-interface/targets as per Move target implementations of NanostackRfPhy into nanostack-interface #13119
• TARGET_Freescale instead of TARGET_NXP as per MIMXRT1050_EVK: Add USB support #13115

Impact of changes

Migration actions required

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

[] No Tests required for this change (E.g docs only update)
[x] Covered by existing mbed-os tests (Greentea or Unittest)
[x] Tests / results supplied as part of this PR

Manual testing: both mbed-os-example-blinky and mbed-os-example-blinky-baremetal compile for KW41Z.

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Reviewers

@MarceloSalazar @evedon

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[ciarmcom]

@LDong-Arm, thank you for your changes.
@MarceloSalazar @evedon @ARMmbed/mbed-os-mesh @ARMmbed/mbed-os-ipcore @ARMmbed/mbed-os-maintainers please review.

[mbed-ci]

Test run: SUCCESS

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