[Skiboot] Make HDAT tests output DTS

[Oliver O'Halloran]

This is a slight rework of Stewart's series found here:
https://patchwork.ozlabs.org/patch/724370/

This re-spin moves the test case data changes into seperate patches so
reviewing the actual code changes doesn't require wading through the noise of
the test case changes.

This series also incorporates my earlier patch that reduces properties larger
than 512 bytes to a <marker, size, checksum> tuple to further reduce
the size of the test cases.