vk: Move anv_color_attachment_view_init() to gen8_state.c

vk: Move anv_color_attachment_view_init() to gen8_state.c

I'd prefer to move anv_CreateAttachmentView() as well, but it's a little
too much generic code to just duplicate for each gen.  For now, we'll
add a anv_color_attachment_view_init() to dispatch to the gen specific
implementation, which we then call from anv_CreateAttachmentView().

Signed-off-by: Kristian Høgsberg Kristensen <kristian.h.kristensen@intel.com>