drm/radeon/kms: forbid big bo allocation (fdo 31708) v3

Forbid allocating buffer bigger than visible VRAM or GTT, also
properly set lpfn field.

v2 - use max macro
   - silence warning
v3 - don't explicitly set range limit
   - use min macro

Cc: stable <stable@kernel.org>

Signed-off-by: Jerome Glisse <jglisse@redhat.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>