configs: at91: sam9x60ek: enable QSPI and SF command

Add the configurations required for enabling QSPI and the SF command
to allow changes to be made dynamically to serial flash devices from
the command line interface.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Tudor Ambarus <tudor.ambarus@microchip.com>