ANDROID: BACKPORT: KVM: arm64: pkvm: Force injection of a data abort on NISV MMIO exit

If a vcpu exits for a data abort with an invalid syndrome, the
expectations are that userspace has a chance to save the day if
it has requested to see such exits.

However, this is completely futile in the case of a protected VM,
as none of the state is available. In this particular case, inject
a data abort directly into the vcpu, consistent with what userspace
could do.

This also helps with pKVM, which discards all syndrome information when
forwarding data aborts that are not known to be MMIO.

Finally, hide the RETURN_NISV_IO_ABORT_TO_USER cap from userspace on
protected VMs, and document this tweak to the API.

Signed-off-by: Marc Zyngier <maz@kernel.org>
Bug: 209580772
[willdeacon@: Drop KVM_CAP_SET_GUEST_DEBUG2 from context]
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I4090c7c266b27776089cac69efd489264ed003cf