anv/image: Scale iview extent by backing image

anv/image: Scale iview extent by backing image

Aligns with formula's presented in Vulkan spec concerning CopyBufferToImage.
18.4 Copying Data Between Buffers and Images

This won't conflict with valid API usage, because:
1) Users are not allowed to create an uncompressed ImageView with a
compressed Image.
see: VkSpec - 11.5 Image Views - VkImageViewCreateInfo's Valid Usage box

2) If users create a differently formatted compressed ImageView with a
compressed Image, the block dimensions will still match.
see: VkSpec - 28.3.1.5 Format Compatibility Classes - Table 28.5