ARM: dts: at91: sama5d2_xplained: Update the pmic node

Due to introducing the new driver - ACT8945A MFD drive,
change the pmic device node to align with the ACT8945A
regulator and charger drivers.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>