bootstrap: Do not set up Git submodules by default

bootstrap: Do not set up Git submodules by default

Building OpenOCD with jimtcl and libjaylink Git submodules is deprecated
and will be removed in the upcoming releases. The remaining 'git2cl'
submodule is only required during the OpenOCD release process.

Only set up Git submodules when the 'with-submodules' argument is used,
for example during the OpenOCD release process or for the transition
period until all submodules are replaced by external dependencies.

We keep the existing 'nosubmodule' argument in order to not break
automatic testing with Jenkins.

Change-Id: Ia4fd765e3a2d6b2c40b084a1ffdf919d5f4f35bb
Signed-off-by: Marc Schink <dev@zapb.de>
Reviewed-on: https://review.openocd.org/c/openocd/+/8381
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>
Reviewed-by: R. Diez <rdiez-2006@rd10.de>