Add testcases for restoreKeys API.

Add a positive and two negative test cases for the restoreKeys
function in DRM vendor plugin.

Test: vts-tradefed run commandAndExit vts -m VtsHalDrmV1_0Target
--primary-abi-only --skip-all-system-status-check
Bug: 34178477
Change-Id: Ia7f323dbd92e7281efa96b9b7d07b85123e819f4