ARM: at91: pm: add sama7g5 ddr phy controller

SAMA7G5 self-refresh procedure accesses also the DDR PHY registers.
Adapt the code so that the at91_dt_ramc() to look also for DDR PHYs,
in case it is mandatory.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210415105010.569620-19-claudiu.beznea@microchip.com