drm/amdgpu: amdgpu_vram_mgr_new(): Clamp lpfn to total vram

The drm_mm allocator tolerated being passed end > mm->size, but the
drm_buddy allocator does not.

Restore the pre-buddy-allocator behavior of allowing such placements.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/3448


Signed-off-by: John Olender <john.olender@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org