KVM: selftests: Map x86's exception_handlers at VM creation, not vCPU setup

Map x86's exception handlers at VM creation, not vCPU setup, as the
mapping is per-VM, i.e. doesn't need to be (re)done for every vCPU.

Reviewed-by: Ackerley Tng <ackerleytng@google.com>
Link: https://lore.kernel.org/r/20240314232637.2538648-12-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>