KVM, SEV: Add KVM_EXIT_SHUTDOWN metadata for SEV-ES

KVM, SEV: Add KVM_EXIT_SHUTDOWN metadata for SEV-ES

If an SEV-ES guest requests termination, exit to userspace with
KVM_EXIT_SYSTEM_EVENT and a dedicated SEV_TERM type instead of -EINVAL
so that userspace can take appropriate action.

See AMD's GHCB spec section '4.1.13 Termination Request' for more details.

Suggested-by: Sean Christopherson <[email protected]>
Suggested-by: Paolo Bonzini <[email protected]>
Cc: [email protected]
Cc: [email protected]
Signed-off-by: Peter Gonda <[email protected]>
Reported-by: kernel test robot <[email protected]>
Message-Id: <20220407210233[email protected]>
[Add documentatino. - Paolo]
Signed-off-by: Paolo Bonzini <[email protected]>