lib/rendercopy_gen7: use vertex struct to describe vb

The idea here is that using a structure to describe a single vertex in
rendercopy improves the readability of vb code, since it allows use of
functions such as sizeof() and offsetof() in place of some of the magic
numbers.
lib/rendercopy_gen7: Simplify rendercopy ps kernel
build: Add CAIRO_FLAGS to the debugger compilation

The library in lib/ exposes <cairo.h> in its main header and thus users
must be able to include it.
tests: add render_copy test with PNG dumps

The purpose of this blit test is to create a set of .png image files,
providing visual feedback for render_copy() testing.
tests: add PNG duplicator render_copy test

The purpose of this blit test is to duplicate an input .png file to a
specified location, allow for visual feedback while testing
render_copy().

  Usage:  gem_render_png_dup <src> <dest>
lib/rendercopy_gen7: Add AUB state annotations