iommu/tegra: gart: cleanup devm_* functions usage

The devm_[kzalloc|ioremap] functions allocates data that are released
when a driver detaches. Thus, there is no reason to explicitly call
devm_[kfree|iounmap] in probe or remove functions.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: Hiroshi Doyu <hdoyu@nvidia.com>
Signed-off-by: Joerg Roedel <joro@8bytes.org>