ARM: 6054/1: AT91: taskit PortuxG20 and Stamp9G20 board support

Both boards share the same board file, as the PortuxG20 is basically an
SBC based on the Stamp9G20.

Signed-off-by: Christian Glindkamp <christian.glindkamp@taskit.de>
Acked-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>