Atmel: move console default platform_device to serial driver

This variable spread on every SoC that is using the atmel_serial.c
driver can be included directly into the latter.

This will allow to compile multiple soc in the same kernel.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: kernel@avr32linux.org