anv: Remove anv_image::surface_type

anv: Remove anv_image::surface_type

When building RENDER_SURFACE_STATE, the driver set
SurfaceType = anv_image::surface_type, which was calculated during
anv_image_init(). This was bad because the value of
anv_image::surface_type was taken from a gen-specific header,
gen8_pack.h, even though the anv_image structure is used for all gens.

Replace anv_image::surface_type with a gen-specific lookup function,
anv_surftype(), defined in gen${x}_state.c.

The lookup function contains some useful asserts that caught some nasty
bugs in anv meta, which were fixed in the previous commit.