scripts: add systemtap script for capturing SEV-ES VMSA

scripts: add systemtap script for capturing SEV-ES VMSA

In general we expect to be able to construct a SEV-ES VMSA
blob from knowledge about the AMD achitectural CPU register
defaults, KVM setup and QEMU setup. If any of this unexpectedly
changes, figuring out what's wrong could be horrible. This
systemtap script demonstrates how to capture the real VMSA
that is used for a SEV-ES as it is booted. The captured data
can be fed into the 'sevctl vmsa show' command in order to
produce formatted info with named registers, allowing a
'diff' to be performed.

This script will need updating for any kernel version that is
not 6.0, to set the correct line numbers.

Reviewed-by: Cole Robinson <crobinso@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>