drm/panfrost: Set DMA max segment size

Since all we do with scatterlists is map them in the MMU, we don't have
any hardware constraints on how they're laid out. Let the DMA layer know
so it won't warn when DMA API debugging is enabled.

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/04371bc36512076b7feee07f854e56b80675d953.1599141563.git.robin.murphy@arm.com