MGF1 Digest setter: Handle case of flag off

In case the MGF1 Digest setter flag is turned off (that is, it is not
possible to specify MGF1 Digests using the new API introduced), then the
old behaviour has to take place.

The old behaviour was to set all primary digests specified, as MGF1 Digests.
This behaviour has been added when the flag isn't set.

Bug: 308378912
Bug: 308069562
Test: atest CtsKeystoreTestCases:android.keystore.cts.CipherTest#testKatBasicWithDifferentProviders CtsKeystoreWycheproofTestCases:RsaOaepTest
Change-Id: I5d4541ce952e1bad7c8fdd55a00176274b0b66f3