We no longer need to generate API documentation for the upstreamed
gvt-g kernel additions so we can remove the doc generation dependency on
the acrn-kernel repo (and all use of the kerneldoc extension). We also
remove GVT-g API documentation and porting guide that are obsolete with
ACRN v2.6 and referenced this API documentation.
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>
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