surfaceflinger: use Vulkan coordinate system

In Vulkan coordinate system, (0, 0) always maps to memory address 0.
In GL coordinate system, (0, 0) maps to the bottom-left corner.  The
two agree when doing offscreen rendering.  But when rendering to a
window, GL maps (0, 0) to memory address (winHeight-1)*rowStride,
because that is where the bottom-left pixel is.

Let's pick the simpler one for RenderEngine in preparation for
multiple backends.  As a result, we don't need yswap when rendering
to offscreen buffers (it is hidden behind the RenderEngine API).  It
also makes no sense to flip Y coordinate for both vertex postions
and the viewing volume.

Test: chrome, youtube, camera, screen rotation, screenshots, recents
Change-Id: I6d6317bac3de6f208700a67e518011362c600ced