KVM: selftests: Extend VM creation's @shape to allow control of VM subtype

KVM: selftests: Extend VM creation's @shape to allow control of VM subtype

Carve out space in the @shape passed to the various VM creation helpers to
allow using the shape to control the subtype of VM, e.g. to identify x86's
SEV VMs (which are "regular" VMs as far as KVM is concerned).

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>
Cc: Vishal Annapurve <vannapurve@google.com>
Cc: Ackerley Tng <ackerleytng@google.com>
Cc: Andrew Jones <andrew.jones@linux.dev>
Cc: Tom Lendacky <thomas.lendacky@amd.com>
Cc: Michael Roth <michael.roth@amd.com>
Tested-by: Carlos Bilbao <carlos.bilbao@amd.com>
Link: https://lore.kernel.org/r/20240223004258.3104051-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>