drm/amdgpu: skip the VMID 0 flush for VRAM

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

drm/amdgpu: skip the VMID 0 flush for VRAM

Clear-on-release only runs on VRAM, which amdgpu_ttm_map_buffer() reaches
via its direct MC address without programming a GART window, yet the wipe
still forces a VMID 0 flush. On GFX11 (e.g. Navi33) that spurious SDMA
flush can wedge the engine; only flush when a GART window is actually used.

v2: Let amdgpu_ttm_map_buffer() return whether the VMID 0 flush is needed,
and drive the clear and copy paths from that. (Christian)
v3: Make the vm_needs_flush output parameter mandatory instead of
allowing NULL. (Christian)

(cherry picked from commit a306e406e570b74318ff7d80e5b07b540ca1d3a9)