build: log submodule update from git-submodule.sh

Print exactly which submodules have been updated, by reusing the logic of
"git-submodule.sh validate" after executing "git submodule update --init'.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
2 files changed