iommu/arm-smmu: log outstanding transactions on sync timeout

On a TLB sync timeout for a given SMMU, dump the outstanding transaction
bitmap for each of its TBUs.  Additionally, introduce a sync_timed_out flag
for each SMMU to be present with the enabling of CONFIG_IOMMU_DEBUG to (1)
ensure that only one thread performs the relevant logging and BUG_ON()
during a sync timeout, and (2) prevent other incoming threads from
triggering further timeouts, which can overwrite the SMMU state data that
would contain information on the initial sync timeout.

Change-Id: I43855ecc51ddd2f3a1a287a39c123784c54ad538
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>