arm/dts: dra72-evm.dts: add HDMI

DRA72 EVM has a HDMI output. This patch adds the device tree nodes
required for HDMI.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: devicetree@vger.kernel.org
Acked-by: Tony Lindgren <tony@atomide.com>