anv: Ignore unused dimensions in vkCreateImage

anv: Ignore unused dimensions in vkCreateImage

We would assert on unused dimensions (eg extent.depth for
VK_IMAGE_TYPE_2D) not being 1, but the specification doesn't put any
constraints on those. For example, for VK_IMAGE_TYPE_1D:

   "If imageType is VK_IMAGE_TYPE_1D, the value of extent.width must be
    less than or equal to the value of
    VkPhysicalDeviceLimits::maxImageDimension1D, or the value of
    VkImageFormatProperties::maxExtent.width (as returned by
    vkGetPhysicalDeviceImageFormatProperties with values of format,
    type, tiling, usage and flags equal to those in this structure) -
    whichever is higher"

We'll fix up the arguments to isl to keep isl strict in what it expects.