i965: Parameterize HiZ code to prepare for adding blitting.

This patch groups together the parameters used by the HiZ functions
into a new data structure, brw_hiz_resolve_params, rather than passing
each parameter individually between the HiZ functions.  This data
structure is a subclass of brw_blorp_params, which represents the
parameters of a general-purpose blit or resolve operation.  A future
patch will add another subclass for blits.

In addition, this patch generalizes the (width, height) parameters to
a full rect (x0, y0, x1, y1), since blitting operations will need to
be able to operate on arbitrary rectangles.  Also, it renames several
of the HiZ functions to reflect the expanded role they will serve.
i965: split gen{6,7}_blorp_exec functions into manageable chunks.

This patch splits up the gen6_blorp_exec and gen7_blorp_exec
functions, which were very long, into simple component functions.
With a few exceptions, there is one function per state packet.

This will allow blit functionality to be added without significantly
complicating the code.
i965: Expose surface setup internals for use by blits.

This patch exposes the functions brw_get_surface_tiling_bits and
gen7_set_surface_tiling, so that they can be re-used when setting up
surface states in gen6_blorp.cpp and gen7_blorp.cpp.
i965/gen6+: Add code to perform blits on the render path ("blorp").

This patch expands the "blorp" component to be able to perform blits
as well as HiZ resolves.  The new blitting code is located in
brw_blorp_blit.cpp.  This includes the necessary fragment shader code
to look up pixels in the source buffer (which is configured as a
texture) and output them to the destination buffer (which is
configured as the render target).

Most of the time the fragment shader code is simple and
straightforward, since it merely has to apply a coordinate offset,
read from the texture, and write to the render target.  However, in
the case of blitting stencil buffers, things are more complicated,
since the GPU stores stencil data using W tiling, and W tiling is not
supported for textures or render targets.  So, we set up the stencil
buffers as Y tiled, and emit fragment shader code that adjusts the
coordinates to account for the difference between W and Y tiling.
Furthermore, since a rectangular region in W tiling does not
necessarily correspond to a rectangular region in Y tiling, we widen
the rectangle primitive to the nearest tile boundary and have the
fragment shader "kill" any pixels that don't fall inside the actual
desired destination rectangle.

All of this is a necessary prerequisite for implementing MSAA, since
we'll need to be able to blit between multisample color, depth, and
stencil buffers and their non-multisampled counterparts, and none of
the existing blitting mechanisms support multisampling.

In addition, the new blitting code should speed up operations where we
previously fell back to software rasterization, such as blitting of
stencil buffers.  The current fallback sequence is: first we try to do
a blit using the hardware blitting engine.  If that fails we try to do
a blit using the render path.  If that also fails then we do the blit
using a meta-op (which may or may not fall back to software
rasterization).

Note that blitting using the render path has some limitations at the
moment: it only supports a few formats, and it doesn't support
mirroring, clipping, or scissoring.  These limitations will be
addressed in future patch series.
i965/gen6: Initial implementation of MSAA.

This patch enables MSAA for Gen6, by modifying intel_mipmap_tree to
understand multisampled buffers, adapting the rendering pipeline setup
to enable multisampled rendering, and adding multisample resolve
operations to brw_blorp_blit.cpp. Some preparation work is also
included for Gen7, but it is not yet enabled.

MSAA support is still fairly preliminary.  In particular, the
following are not yet supported:
- Fully general blits between MSAA and non-MSAA buffers.
- Formats other than RGBA8, DEPTH24, and STENCIL8.
- Centroid interpolation.
- Coverage parameters (glSampleCoverage, GL_SAMPLE_ALPHA_TO_COVERAGE,
  GL_SAMPLE_ALPHA_TO_ONE, GL_SAMPLE_COVERAGE, GL_SAMPLE_COVERAGE_VALUE,
  GL_SAMPLE_COVERAGE_INVERT).

Fixes piglit tests "EXT_framebuffer_multisample/accuracy" on
i965/Gen6.
Blorp: implement mirroring.