thunderbolt: Remove useless DMA-32 fallback configuration

As stated in [1], dma_set_mask() with a 64-bit mask never fails if
dev->dma_mask is non-NULL.
So, if it fails, the 32 bits case will also fail for the same reason.

Simplify code and remove some dead code accordingly.

While at it, include directly <linux/dma-mapping.h> instead on relying on
indirect inclusion.

[1]: https://lkml.org/lkml/2021/6/7/398



Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>