gpu: nvgpu: add API to query page table memhandles

Add API to query all memhandles used for pde and pte.
- Some direct pde/pte allocation should also add entry to the pd-cache
full list.
- Add OS API for querying MemServ handle from nvgpu_mem.
- Traverse through all pd-cache partial and full lists to get memhandles
for all pde/pte buffers.

Jira NVGPU-8284

Change-Id: I8e7adf1be1409264d24e17501eb7c32a81950728
Signed-off-by: Shashank Singh <shashsingh@nvidia.com>
Reviewed-on: https://git-master.nvidia.com/r/c/linux-nvgpu/+/2735657
Reviewed-by: svc-mobile-coverity <svc-mobile-coverity@nvidia.com>
Reviewed-by: Vaibhav Kachore <vkachore@nvidia.com>
GVS: Gerrit_Virtual_Submit <buildbot_gerritrpt@nvidia.com>

userspace/units/mm/allocators/buddy_allocator/buddy_allocator.c

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2020, NVIDIA CORPORATION.  All rights reserved.
+ * Copyright (c) 2019-2022, NVIDIA CORPORATION.  All rights reserved.
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
@@ -96,7 +96,9 @@ static struct vm_gk20a *init_vm_env(struct unit_module *m, struct gk20a *g,
 	aperture_size = GK20A_PMU_VA_SIZE;
 
 	flags |= GPU_ALLOC_GVA_SPACE;
-
+	if (nvgpu_pd_cache_init(g) != 0) {
+		unit_err(m, "PD cache initialization failed\n");
+	}
 	/* Init vm with big_pages disabled */
 	test_vm = nvgpu_vm_init(g, g->ops.mm.gmmu.get_default_big_page_size(),
 				   low_hole,