Apparently, we've been requiring a 4K alignment for internally allocated clear color addresses to work around some unknown issues. There's a comment to that effect in iris_resource_create_with_modifiers().
When importing a dmabuf and tacking on an additional clear color BO, we only required an alignment of 1. This wasn't a problem for a long time because all BO allocations were naturally aligned to the 4K page size.
However, once we enabled suballocation, we were able to allocate "BOs" at 256B granularity, making this no longer 4K aligned. Increase the alignment requirement to 4K to match the behavior of our normal allocations and also our previous behavior.
Fixes Piglit's ext_image_dma_buf_import-intel-modifiers.