arm64: dts: keembay: Add device tree for Keem Bay EVM board

Add initial device tree for Keem Bay EVM board. With this minimal device
tree the board boots fine using an initramfs image.

Link: https://lore.kernel.org/r/20200717090414.313530-6-daniele.alessandrelli@linux.intel.com


Reviewed-by: Dinh Nguyen <dinguyen@kernel.org>
Signed-off-by: Daniele Alessandrelli <daniele.alessandrelli@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>