AT91SAM9260EK: Normalize SPI timings

This patch changes the SPI timings to closely match the ones
used by the Linux kernel and the Atmel's own bootstrap project.

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