Add a @can_yield param to __walk_slot_rmaps() to control whether or not
dropping mmu_lock and conditionally rescheduling is allowed.  This will
allow using __walk_slot_rmaps() and thus cond_resched() to handle
mmu_notifier invalidations, which usually allow blocking/yielding, but not
when invoked by the OOM killer.

Link: https://lore.kernel.org/r/20240809194335.1726916-12-seanjc@google.comSigned-off-by: Sean Christopherson <seanjc@google.com>