[Intel-gfx] Exporting pipe from kernel for tear-free XV with KMS

[Carl Worth]

Just after we released xf86-video-intel 2.7.0 and claimed to have
tear-free video playing, people noticed a couple of cases where that
doesn't work:

        1. When a compositing manager is running

        2. When KMS is enabled

For the compositing-manager case, we still need to write new code to
allow applications to ask for a tear-free region copy. I haven't done
any work on this case yet.

For the KMS case, the problem was simply a matter of allowing the X
driver to discover the pipe number for a given CRTC, (which only the
kernel driver was aware of). I'm posting now a patch series for that,
which results in nice, tear-free video with KMS, (assuming no
compositing manager of course).

This series touches the i915 driver in the Linux kernel, libdrm, and
the xf86-video-intel driver. I've previously done little to no work in
those first two projects, so if I've gotten anything wrong, (coding
style, wrong mailing list for patches, etc.), just let me know.

Within the patch emails I've made some comments about some concerns I
have with the series. Most are minor (naming of functions within the
kernel driver), but one is significant: What checks, if any, should I
make so that the X driver acts in a graceful way given an older libdrm
without the new function?

-Carl