gpu: docs: amdgpu.rst: get rid of wrong kernel-doc markups

gpu: docs: amdgpu.rst: get rid of wrong kernel-doc markups

As reported by kernel-doc:
    ./drivers/gpu/drm/amd/amdgpu/amdgpu_xgmi.c:1: warning: no structured comments found
    ./drivers/gpu/drm/amd/amdgpu/amdgpu_ras.c:1: warning: no structured comments found

Those files only contain

	/**
	 * DOC:
	 */

markups, but they're included twice there: one to parse
such markup, and another one to parse internal functions.

In the case of amdgpu_xgmi.c, as it has just one such
markup, we can simply include the file once, and let it
parse the entire file without passing arguments to kernel-doc.

This should place everything altogether.

For amdgpu_ras.c, however, we need to remove the kernel-doc
with just internal. This should be re-introduced if this
file ever gets new non-DOC markups.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/bd070923591ae54f9587e7407b6291ac116952b2.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>