iommu/tegra-smmu: Use devm_bitmap_zalloc when applicable

'smmu->asids' is a bitmap. So use 'devm_kzalloc()' to simplify code,
improve the semantic of the code and avoid some open-coded arithmetic in
allocator arguments.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Acked-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/2c0f4da80c3b5ef83299c651f69a563034c1c6cb.1632661557.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Joerg Roedel <jroedel@suse.de>