ARM: at91: dts: request only spi cs-gpios used on sama5d3x cpu module

Instead of requesting all available spi cs-gpios, request only the ones used on
the board, in our case on the cpu module.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>