drm/msm: Fix gen_header.py for older python3 versions

drm/msm: Fix gen_header.py for older python3 versions

The gen_header.py script is failing for older versions of python3 such
as python 3.5. Two issues observed with python 3.5 are ...

 1. Python 3 versions prior to 3.6 do not support the f-string format.
 2. Early python 3 versions do not support the 'required' argument for
    the argparse add_subparsers().

Fix both of the above so that older versions of python 3 still work.

Fixes: 8f7abf0b86fe ("drm/msm: generate headers on the fly")
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/589427/
Link: https://lore.kernel.org/r/20240412165407.42163-1-jonathanh@nvidia.com
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>