Keystore: Attestation fix in non AOSP builds

After adding attestation properties for AOSP/GSI builds their comparison
in Spi layer missed one condition. If these values were not set they were assigned
as Build.UNKNOWN. Hence additional check is added in Spi layer.

Bug: 267643193
Test: atest CtsKeystoreTestCases:android.keystore.cts.KeyAttestationTest CtsKeystoreTestCases:DeviceOwnerKeyManagementTest
Change-Id: I5b3ef0a308bbb12bc4cac2efcf04468f65db1ef8