drm/i915: Fix missing docbook chapters for i915 uapi.

I noticed when grepping for DOC: that those were defined
in the header, but not actually used. Fix it by removing
all chapters and the internal annotation, so the docbook
generated chapters are used.

This reverts the changes to driver-uapi.rst by the referenced commit
57772953

 ("drm/i915: Document the Virtual Engine uAPI")

Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210715120842.806605-1-maarten.lankhorst@linux.intel.com
Fixes: 57772953

 ("drm/i915: Document the Virtual Engine uAPI")
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>