shell: Add pushd/popd functions
shell: Add pushd/popd functions

Signed-off-by: Esben Haabendal <da90c138e4a9573086862393cde34fa33d74f6e5@haabendal.dk>

XD-embedded/xd-tool,XD-embedded/xd-tool,esben/xd-tool,esben/xd-tool