i965g: add GEN6 GPE

GEN6 GPE (Graphics Processing Engine) is a low-level interface to emit 3D
commands and states.
i965g: add GEN6 3D context

The GEN6 3D context is a high-level interface to emit 3D commands and states.
It uses GEN6 GPE to do the real work.
i965g: hook up pipe context 3D functions
i965g: add support for time/occlusion/primitive queries
i965g: hook up pipe context video functions

This just hooks them up with auxiliary/vl layer.
i965g: hook up pipe context GPGPU functions

This just adds a stub.
i965g: add a toy shader compiler

This is a simple shader compiler that performs almost zero optimizations.  The
generated code is usually much larger comparing to that generated by i965.
The generated code also requires many more registers.

Function-wise, it lacks register spilling and does not support most TGSI
indirections.  Other than those, it works alright.
i965g: compile VS/GS/FS with the toy compiler
i965g: add the driver to various targets

Add i965g to targets/egl-static and targets/pipe-loader.  Also the new target
dri-i965.
i965g: add the driver to --with-gallium-drivers