dma-buf: add DMA_RESV_USAGE_KERNEL v3

Add an usage for kernel submissions. Waiting for those are mandatory for
dynamic DMA-bufs.

As a precaution this patch also changes all occurrences where fences are
added as part of memory management in TTM, VMWGFX and i915 to use the
new value because it now becomes possible for drivers to ignore fences
with the WRITE usage.

v2: use "must" in documentation, fix whitespaces
v3: separate out some driver changes and better document why some
    changes should still be part of this patch.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220407085946.744568-5-christian.koenig@amd.com