KeyMint VTS: add missing purpose/algo

Test was producing an invalid set of parameters in a different way than
intended.

Bug: 197222749
Test: VtsAidlKeyMintTargetTest
Merged-In: I07f706fec81d91e8eee9c0561428142559c54f12
Change-Id: I07f706fec81d91e8eee9c0561428142559c54f12
Ignore-AOSP-First: this is a manual cross-merge