configs: at91: sam9x60: Add required configs for the USB clock

Add the configs required to use the SAM9X60's USB clock.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/20221223123313.362676-6-sergiu.moga@microchip.com