ARM: dts: at91: sama5d2_xplained: Add charger node

Add the charger device node as a sub-device of act8945a mfd, move
the charger's properties in the node, and replace the
"active-semi,irq_gpios" with the "interrupts" property to denote
the act8945a charger's irq.

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