ANDROID: KVM: arm64: relay entropy requests from protected guests directly to secure

As pKVM does not trust the host, it should not be involved in the
handling of, or be able to observe the response to entropy requests
issues by protected guests.

When an SMC-based implementation of the ARM SMCCC TRNG interface is
present, pass any HVC-based requests directly on to the secure firmware.

Co-developed-by: Ard Biesheuvel <ardb@google.com>
Signed-off-by: Ard Biesheuvel <ardb@google.com>
Signed-off-by: Will Deacon <will@kernel.org>
Bug: 278749606
Change-Id: Ica492ce49fd059a62ecc31bb7ac13c9adb773a08