at91: Use "pclk" as con_id on at91cap9 and at91rm9200

Hello,

I am not 100% sure this is the right thing to do, but it makes the
atmel-ssc driver happy on my at91rm9200 board.

This unifies the con_id across all at91 machines.

The atmel-ssc driver expects the con_id to be "pclk" or it will fail probing.

Signed-off-by: Joachim Eastwood <joachim.eastwood@jotron.com>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>