ARM: dts: am335x-chili*: add chiliSOM and chiliboard DTS files

Import chiliSOM and chiliboard dts files from Linux v4.19. They will
be used after transition to driver model and device-tree based boot.

Signed-off-by: Marcin Niestroj <m.niestroj@grinn-global.com>
Reviewed-by: Tom Rini <trini@konsulko.com>