Use a common u-boot.lds file across all AT91CAP9/AT91SAM9 platforms

All the AT91CAP9/AT91SAM9 boards have the same linker script. The patch
below avoids the duplication of u-boot.lds by putting the file in the
cpu directory instead of the board one.

Signed-off-by: Stelian Pop <stelian@popies.net>
Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>