Fixed compile error on targets where DEVICE_SPI or DEVICE_INTERRUPTIN are defined but not both

[talorion]

Summary of changes

Fixed a missmatch in the guards in NanostackRfPhyAtmel.h and NanostackRfPhyAT86RF215.cpp
the problem is better described in #13299
basically when either DEVICE_SPI or DEVICE_INTERRUPTIN are defined but not both we running Into the problem that the guards in NanostackRfPhyAtmel.h do not match the ones in NanostackRfPhyAT86RF215.cpp
I added a guard in rfbits.h which checks if DEVICE_SPI is defined since the file clearly requires SPI.

Impact of changes

on some custom targets where DEVICE_SPI or DEVICE_INTERRUPTIN are defined but not both the build fails

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

[] 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]

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

[0xc0170]

Could you clean the commit history - 2 merge commits could be eliminated if rebased.

[0xc0170]

Thanks for fixing the issue. We will review