ARM: at91: remove default values for PMC_PLL_ACR

ARM: at91: remove default values for PMC_PLL_ACR

Remove default values for PMC PLL Analog Control Register(ACR) as the
values are specific for each SoC and PLL and load them from PLL
characteristics structure

Co-developed-by: Andrei Simion <andrei.simion@microchip.com>
Signed-off-by: Andrei Simion <andrei.simion@microchip.com>
Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
[nicolas.ferre@microchip.com: fix pll acr write sequence, preserve val]
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>