iommu/arm-smmu-v3: Simplify memory allocation

Use devm_bitmap_zalloc() instead of hand writing it.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/598bd905103dcbe5653a54bb0dfb5a8597728214.1644274051.git.christophe.jaillet@wanadoo.fr


Signed-off-by: Will Deacon <will@kernel.org>