[microNPU][ETHOSU] Fix minimum buffer size

[Aleksei-grovety]

Fix minimum buffer size for DMA operations according to alignment.

cc @neildhickey, @lhutton1, @ekalda, @leandron

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• cc @Mousius, @leandron _{See #10317 for details}

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[ekalda]

Thanks @Aleksei-grovety! I think a test would be good there as well.

[Aleksei-grovety]

I added a test for this case.

[ekalda]

LGTM, thanks @Aleksei-grovety!