i965/blorp: Fixup scissoring of blits to window system buffers.

i965/blorp: Fixup scissoring of blits to window system buffers.

This patch modifies the order of operations in the blorp engine so
that clipping and scissoring are performed before adjusting the
coordinates to account for the difference in origin convention between
window system buffers and framebuffer objects.  Previously, we would
do clipping and scissoring after adjusting for origin conventions, so
we would get scissoring wrong in window system buffers.

Fixes Piglit test "fbo-scissor-blit window".

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>