iommu/arm-smmu-v3: Replace arm_vsmmu_alloc with arm_vsmmu_init

iommu/arm-smmu-v3: Replace arm_vsmmu_alloc with arm_vsmmu_init

To ease the for-driver iommufd APIs, get_viommu_size and viommu_init ops
are introduced.

Sanitize the inputs and report the size of struct arm_vsmmu on success, in
arm_smmu_get_viommu_size().

Place the type sanity at the last, becase there will be soon an impl level
get_viommu_size op, which will require the same sanity tests prior. It can
simply insert a piece of code in front of the IOMMU_VIOMMU_TYPE_ARM_SMMUV3
sanity.

The core will ensure the viommu_type is set to the core vIOMMU object, and
pass in the same dev pointer, so arm_vsmmu_init() won't need to repeat the
same sanity tests but to simply init the arm_vsmmu struct.

Remove the arm_vsmmu_alloc, completing the replacement.

Link: https://patch.msgid.link/r/64e4b4c33acd26e1bd676e077be80e00fb63f17c.1749882255.git.nicolinc@nvidia.com
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Reviewed-by: Pranjal Shrivastava <praan@google.com>
Acked-by: Will Deacon <will@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>