ANDROID: KVM: arm64: Pass the pagetable struct as an argument to the freewalker

Extend the scope of the stage2_freewalker by passing the pgt instead of
the mm_ops callbacks. This will later be used by the stage2_pte_is_counted
function.

Bug: 222044487
Signed-off-by: Sebastian Ene <sebastianene@google.com>
Change-Id: I390661eb106cbdb863cbb1832e39ec155c439091