drm/msm: import gen_header.py script from Mesa

Import the gen_headers.py script from Mesa, commit b5414e716684
("freedreno/registers: Add license header"). This script will be used to
generate MSM register files on the fly during compilation.
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/585864/
Link: https://lore.kernel.org/r/20240401-fd-xml-shipped-v5-10-4bdb277a85a1@linaro.org