ARM: dts: turris-omnia: enable HW buffer management

The buffer manager is available on Turris Omnia but needs to be
described in device-tree to be used.

Signed-off-by: Marek Behún <kabel@kernel.org>
Fixes: 26ca8b52

 ("ARM: dts: add support for Turris Omnia")
Cc: linux-arm-kernel@lists.infradead.org
Cc: Uwe Kleine-König <uwe@kleine-koenig.org>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Gregory CLEMENT <gregory.clement@bootlin.com>
Cc: Andreas Färber <afaerber@suse.de>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: devicetree@vger.kernel.org
Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>