drivers: iommu: Don't acquire stream_map_mutex in testbus dump path

In the testbus dumping path after acquiring tesbus_lock which is a
spinlock, to get the sid stream_map_mutex is acquired, this sequence
would result in calling sleep from atomic context so, to avoid
this get sid from fwspec and avoid acquiring stream_map_mutex.
Also move testbus dumping code to arm_smmu_testbus_dump function.

Fixes: 9c2fbeb6eef2 ("drivers: iommu: dump testbus output on tlb_sync timeouts")
Change-Id: Ib64d268a7278771717c3bd355a10f31aa21fe185
Signed-off-by: Vijayanand Jitta <vjitta@codeaurora.org>