clk: at91: sam9x60: Add initial setup of UPLL and USBCK rates

In order for some of the functionalities, such as the USB clocks,
to work properly we need some clocks to be properly initialised
at the very beginning of booting.

Signed-off-by: Sergiu Moga <sergiu.moga@microchip.com>
Reviewed-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>