Secretkeeper implementation: in-HAL/nonsecure impl

Create the default/reference implementation of Secretkeeper HAL. Status
quo, this is non-secure implementation. In reality, the HAL should be
backed by a privileged component such a trusted app.

Bug: 291224769
Test: Topic includes VTS
Change-Id: I6a4ad50482d537f5438de6201275f4020cd827df