ARM: at91: pm: save and restore ACR during PLL disable/enable

ARM: at91: pm: save and restore ACR during PLL disable/enable

Add a new word in assembly to store ACR value during the calls
to at91_plla_disable/at91_plla_enable macros and use it.

Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
[cristian.birsan@microchip.com: remove ACR_DEFAULT_PLLA loading]
Signed-off-by: Cristian Birsan <cristian.birsan@microchip.com>
Link: https://lore.kernel.org/r/20250827145427.46819-4-nicolas.ferre@microchip.com
Reviewed-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>