drm/etnaviv: rename etnaviv_iommu_domain_restore to etnaviv_iommuv1_restore

This function has external visibility and only handles the Vivant IOMMU
version 1. Rename to make this more clear and allow a clear separation
of the different IOMMU versions.

Also drop the domain parameter, as we can infer it from the GPU we are
dealing with.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>