pm: at91: pm_slowclock: move disabling the DDR clock after the code to disable the DDRC peripheral clock

It is verified on the SAMA5D4-EK that it is more reliable to disable DDR clock.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
ARM: dts: at91-sama5d4_xplained: add pinctrl state dtsi file

Allow the pin controller to handle and set the state of the pins to:
* "default" on boot, resume and before performing an transfer.
* "sleep" on suspend.

This should make it possible to optimize energy usage for the pins
both for the suspend/resume cycle.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>