For kernel driver BOs, be explicit about whether we need
vram access up front.  This avoids unecessary migrations and
avoids using visible vram for buffers were it's not needed.

v2: line wrap fixes
Reviewed-by: NChristian König <christian.koenig@amd.com>
Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>