iommu/tegra: smmu: Fix unsleepable memory allocation

allo_pdir() is called in smmu_iommu_domain_init() with spin_lock
held. memory allocations in it have to be atomic/unsleepable.

Signed-off-by: Hiroshi DOYU <hdoyu@nvidia.com>
Reported-by: Chris Wright <chrisw@sous-sol.org>
Acked-by: Chris Wright <chrisw@sous-sol.org>
Cc: stable@vger.kernel.org
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>