docs: sphinx/kernel_abi: avoid warnings during Sphinx module init

docs: sphinx/kernel_abi: avoid warnings during Sphinx module init

Sphinx logging system doesn't like warnings during module load,
as it understands that such logs are produced at the wrong time:

	WARNING: while setting up extension automarkup: /sys/devices/system/cpu/cpuX/topology/physical_package_id is defined 2 times: /new_devel/v4l/docs/Documentation/ABI/stable/sysfs-devices-system-cpu:27; /new_devel/v4l/docs/Documentation/ABI/testing/sysfs-devices-system-cpu:70
	WARNING: while setting up extension automarkup: /sys/devices/system/cpu/cpuX/topology/ppin is defined 2 times: /new_devel/v4l/docs/Documentation/ABI/stable/sysfs-devices-system-cpu:89; /new_devel/v4l/docs/Documentation/ABI/testing/sysfs-devices-system-cpu:70

So, use a function to allocate/process ABI files and use it to
be called at kernel_abi.py, as automarkup also needs it to
produce the right cross-references.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/b0e79dc60d556e3b39fa6774d3b7bf734b73f352.1739182025.git.mchehab+huawei@kernel.org