KVM: arm64: Add tracing capability for the nVHE/pKVM hyp

KVM: arm64: Add tracing capability for the nVHE/pKVM hyp

There is currently no way to inspect or log what's happening at EL2
when the nVHE or pKVM hypervisor is used. With the growing set of
features for pKVM, the need for tooling is more pressing. And tracefs,
by its reliability, versatility and support for user-space is fit for
purpose.

Add support to write into a tracefs compatible ring-buffer. There's no
way the hypervisor could log events directly into the host tracefs
ring-buffers. So instead let's use our own, where the hypervisor is the
writer and the host the reader.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Link: https://patch.msgid.link/20260309162516.2623589-24-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>