Add a common board dtsi for use by Milk-V Mars CM and Milk-V Mars CM Lite. Signed-off-by: E Shattow <e@freeshell.de> Signed-off-by: Conor Dooley <conor.dooley@microchip.com> [ upstream commit: 651b30c58775e334c79aa3ecd44a3d98ac201db2 ] (cherry picked from commit 034af14dcd1e6dbfa4f41a340b6d92b054604858)