configs: sam9x60ek: enable CONFIG_CPU

Enable CONFIG_CPU for SAM9X60EK configs.

Reported-by: Eugen Hristev <eugen.hristev@microchip.com>
Fixes: a6486228 ("clk: at91: sam9x60: add support compatible with
CCF")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>