docs/bpf: Fix sphinx warnings for cpumap

Sphinx version >=3.1 warns about duplicate function declarations in the
CPUMAP documentation. This is because the function name is the same for
kernel and user space BPF progs but the parameters and return types
they take is what differs. This patch moves from using the ``c:function::``
directive to using the ``code-block:: c`` directive. The patches also fix
the indentation for the text associated with the "new" code block delcarations.
The missing support of c:namespace-push:: and c:namespace-pop:: directives by
helper scripts for kernel documentation prevents using the ``c:function::``
directive with proper namespacing.

Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20221123092321.88558-2-mtahhan@redhat.com

bpf, docs: Fixup cpumap sphinx >= 3.1 warning

Fixup bpf_map_update_elem() declaration to use a single line.

Reported-by: Akira Yokosawa <akiyks@gmail.com>
Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Akira Yokosawa <akiyks@gmail.com>
Acked-by: Stanislav Fomichev <sdf@google.com>
Link: https://lore.kernel.org/bpf/20221113103327.3287482-1-mtahhan@redhat.com

docs/bpf: Document BPF_MAP_TYPE_CPUMAP map

Add documentation for BPF_MAP_TYPE_CPUMAP including
kernel version introduced, usage and examples.

Co-developed-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Maryam Tahhan <mtahhan@redhat.com>
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20221107165207.2682075-2-mtahhan@redhat.com