ARM: dts: at91: sama5d2: add ETM and ETB nodes

Add node to support SAMA5D2 Embedded Trace Macrocell and Embedded
Trace Buffer.

This patch depends on coresight-etm3x: Add ARM ETM-A5 peripheral ID
for proper coresight functionality.
It also depends on clocksource: timer-atmel-pit: enable mck to not
stall SAMA5D2 on bootup.

Signed-off-by: Olivier Schonken <olivier.schonken@gmail.com>
Acked-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>