ARM: dts: am437x: cm-t43: add basic support for sbc-t43

Add basic support for SBC-T43: a CM-T43 based single board computer.
CM-T43 is an AM437x based System-on-Module designed to serve as a building
block in embedded applications. SBC-T43 is composed of CM-T43 module on
top of the SB-SOM-T43 baseboard.
Basic support includes UART, GPIO, and I2C.

Signed-off-by: Nikita Kiryanov <nikita@compulab.co.il>
Acked-by: Rob Herring <robh@kernel.org>
Cc: Tony Lindgren <tony@atomide.com>
Cc: Benoit Cousson <bcousson@baylibre.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Igor Grinberg <grinberg@compulab.co.il>
Cc: Dmitry Lifshitz <lifshitz@compulab.co.il>
Cc: Ian Campbell <ijc+devicetree@hellion.org.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>