Revert "drm/amdgpu: move internal vram_mgr function into the C file"

This reverts commit 708d19d9.

This is part of a revert of the following commits:
commit 708d19d9 ("drm/amdgpu: move internal vram_mgr function into the C file")
commit 5e3f1e77 ("drm/amdgpu: fix start calculation in amdgpu_vram_mgr_new")
commit c9cad937 ("drm/amdgpu: add drm buddy support to amdgpu")

[WHY]
Few users reported garbaged graphics as soon as x starts,
reverting until this can be resolved.

Signed-off-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220708093047.492662-1-Arunpravin.PaneerSelvam@amd.com