target/arm: Add section labels for "Data Processing (register)"

target/arm: Add section labels for "Data Processing (register)"

At the same time, use ### to separate 3rd-level sections.
We already use ### for 4.1.92 Data Processing (immediate),
but not the two following two third-level sections:
4.1.93 Branches, and 4.1.94 Loads and stores.

Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20241211163036.2297116-2-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>