iommu/tegra-smmu: Add locking around mapping operations

iommu/tegra-smmu: Add locking around mapping operations

The mapping operations of the Tegra SMMU driver are subjected to a race
condition issues because SMMU Address Space isn't allocated and freed
atomically, while it should be. This patch makes the mapping operations
atomic, it fixes an accidentally released Host1x Address Space problem
which happens while running multiple graphics tests in parallel on
Tegra30, i.e. by having multiple threads racing with each other in the
Host1x's submission and completion code paths, performing IOVA mappings
and unmappings in parallel.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Tested-by: Thierry Reding <treding@nvidia.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20200901203730.27865-1-digetx@gmail.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>