anv/meta: Add the beginnings of a blitter API

anv/meta: Add the beginnings of a blitter API

This API is designed to be an abstraction that sits between the VkCmdCopy
commands and the hardware.  The idea is that it is simple enough that it
*should* be implementable using the blitter but with enough extra data that
we can implement it with the 3-D pipeline efficiently.  One design
objective is to allow the user to supply enough information that we can
handle most blit operations with a single draw call even if they require
copying multiple rectangles.