drm/doc: Rename docbook to gpu.tmpl

DRM is a lot more than a direct rendering manager nowadays, and there's
also a bunch of things worth documenting for gpu driver developers
outside of drivers/gpu/drm, like vgaarb, vga_switcheroo or the various
hardware buses like host1x and ipu-v3.

To avoid further confusion let's rename the top-level to reflect
reality.

And yes I'm already looking forward to when we need to replace the G
in GPU with a * ;-)

Inspired by a thread with Lukas since he refused to include the
vga_switcheroo docs into the drm docs because it's not drm.

Cc: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
[Lukas: Drop BUG() easter egg in i915_gem_execbuffer.c spotted by Jani
and fix typos in commit message.]
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Acked-by: Dave Airlie <airlied@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Documentation/DocBook/Makefile

@@ -14,7 +14,7 @@ DOCBOOKS := z8530book.xml device-drivers.xml \
 	    genericirq.xml s390-drivers.xml uio-howto.xml scsi.xml \
 	    80211.xml debugobjects.xml sh.xml regulator.xml \
 	    alsa-driver-api.xml writing-an-alsa-driver.xml \
-	    tracepoint.xml drm.xml media_api.xml w1.xml \
+	    tracepoint.xml gpu.xml media_api.xml w1.xml \
 	    writing_musb_glue_layer.xml crypto-API.xml iio.xml
 
 include Documentation/DocBook/media/Makefile

Documentation/DocBook/gpu.tmpl

@@ -4,7 +4,7 @@
 
 <book id="drmDevelopersGuide">
   <bookinfo>
-    <title>Linux DRM Developer's Guide</title>
+    <title>Linux GPU Driver Developer's Guide</title>
 
     <authorgroup>
       <author>