i965: Implement CopyTexSubImage2D via BLORP (and use it by default).

The BLT engine has many limitations.  Currently, it can only blit
X-tiled buffers (since we don't have a kernel API to whack the BLT
tiling mode register), which means all depth/stencil operations get
punted to meta code, which can be very CPU-intensive.

Even if we used the BLT engine, it can't blit between buffers with
different tiling modes, such as an X-tiled non-MSAA ARGB8888 texture
and a Y-tiled CMS ARGB8888 renderbuffer.  This is a fundamental
limitation, and the only way around that is to use BLORP.

Previously, BLORP only handled BlitFramebuffer.  This patch adds an
additional frontend for doing CopyTexSubImage.  It also makes it the
default.  This is partly to increase testing and avoid hiding bugs,
and partly because the BLORP path can already handle more cases.  With
trivial extensions, it should be able to handle everything the BLT can.

This helps PlaneShift massively, which tries to CopyTexSubImage2D
between depth buffers whenever a player casts a spell.  Since these
are Y-tiled, we hit meta and software ReadPixels paths, eating 99% CPU
while delivering ~1 FPS.  This is particularly bad in an MMO setting
because people cast spells all the time.

It also helps Xonotic in 4X MSAA mode.  At default power management
settings, I measured a 6.35138% +/- 0.672548% performance boost (n=5).
(This data is from v1 of the patch.)

No Piglit regressions on Ivybridge (v3) or Sandybridge (v2).

v2: Create a fake intel_renderbuffer to wrap the destination texture
    image and then reuse do_blorp_blit rather than reimplementing most
    of it.  Remove unnecessary clipping code and conditional rendering
    check.

v3: Reuse formats_match() to centralize checks; delete temporary
    renderbuffers.  Reorganize the code.

v4: Actually copy stencil when dealing with separate stencil buffers but
    packed depth/stencil formats.  Tested by a new Piglit test.

NOTE: This is a candidate for the 9.1 branch.

Signed-off-by: Kenneth Graunke <[email protected]>
Reviewed-by: Paul Berry <[email protected]> [v4]
Reviewed-by: Ian Romanick <[email protected]> [v3]
Reviewed-and-tested-by: Carl Worth <[email protected]> [v2]
Tested-by: Martin Steigerwald <[email protected]> [v3]

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