Say Y here to (by default) disable bypass streams such that
incoming transactions from devices that are not attached to
an iommu domain will report an abort back to the device and
will not be allowed to pass through the SMMU.

Any old kernels that existed before this KConfig was
introduced would default to _allowing_ bypass (AKA the
equivalent of NO for this config). However the default for
this option is YES because the old behavior is insecure.

There are few reasons to allow unmatched stream bypass, and
even fewer good ones. If saying YES here breaks your board
you should work on fixing your board. This KConfig option
is expected to be removed in the future and we'll simply
hardcode the bypass disable in the code.

NOTE: the kernel command line parameter
'arm-smmu.disable_bypass' will continue to override this
config.