linuxkpi: Support non-NULL zero-size pointers

[dumbbell]

Summary

DRM drivers set some pointers to ZERO_SIZE_PTR directly (without allocating anything), to treat pointers which were "initialized" (set to ZERO_SIZE_PTR) with no memory allocation like really allocated pointers. NULL isn't used because it represents a third state.

This is part of the update of the DRM drivers to Linux 5.17.