drm/xe/pf: Clear all LMTT pages on alloc

In the Linux kernel, the following vulnerability has been resolved:

drm/xe/pf: Clear all LMTT pages on alloc

Our LMEM buffer objects are not cleared by default on alloc and during VF provisioning we only setup LMTT PTEs for the actually provisioned LMEM range. But beyond that valid range we might leave some stale data that could either point to some other VFs allocations or even to the PF pages.

Explicitly clear all new LMTT page to avoid the risk that a malicious VF would try to exploit that gap.

While around add asserts to catch any undesired PTE overwrites and low-level debug traces to track LMTT PT life-cycle.

(cherry picked from commit 3fae6918a3e27cce20ded2551f863fb05d4bef8d)