selftest/devtool: add devtool upgrade selftest for recipes with git submodules

selftest/devtool: add devtool upgrade selftest for recipes with git submodules

Tests [YOCTO #15943]

Move code from test_devtool_upgrade_git() into separate, local function.
Add a test_devtool_upgrade_gitsm() selftest for devtool.
Add recipes for testing gitsm components.

Signed-off-by: Tobias Pistora <pistora.tobias@gmail.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>