[Intel-gfx] RFC Fast batch and relocation handling for i965

[Chris Wilson]

Relocation processing is a significant overhead of heavy batches. The
kernel tries to make this as cheap as possible by avoiding as much work
as possible, but to be truly lazy requires userspace to construct its
batches and relocation trees in a convenient manner for processing.

Kristian made an attempt to enable libdrm_intel to supply its
execbuffers in this format,

http://lists.freedesktop.org/archives/intel-gfx/2015-January/058550.html

This is my batchmgr concept from that thread.
-Chris