aux/vk: allow VkImageViewUsageCreateInfo in Vulkan 1.1
Some drivers do not advertise support for VK_KHR_maintenance2 in Vulkan 1.1, because it has been promoted to core.
This caused a validation error on compositors that use Vulkan 1.1 because the scratch image is allocated with unorm format and STORAGE usage: an image view with srgb format can not be created with STORAGE usage on many GPUs.