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>
Bug: 357781595
Change-Id: Ica492ce49fd059a62ecc31bb7ac13c9adb773a08
Signed-off-by: Ard Biesheuvel <ardb@google.com>
Signed-off-by: Will Deacon <will@kernel.org>