iommu: dart: Support a variable number of TTBRs per stream

T8110 only has one TTBR per stream, so un-hardcode that.

Reviewed-by: Sven Peter <sven@svenpeter.dev>
Signed-off-by: Hector Martin <marcan@marcan.st>
Link: https://lore.kernel.org/r/20230113105029.26654-5-marcan@marcan.st


Signed-off-by: Joerg Roedel <jroedel@suse.de>