Currently, VM pause/resume/snapshot paths invoke architecture specific
bits for guest clock udpates which ideally belongs to hypervisor layer.
Route it through the snapshot_clock()/restore_clock() pair added in the
previous commit instead, so the VMM no longer depends on an architecture
specific clock API and the upcoming aarch64 backend can hook the same
path without a parallel branch in vm.rs.
Signed-off-by: Atish Patra <atishp@meta.com>