ARM: at91: sama7: introduce sama7 SoC family

Introduce new family of SoCs, sama7, and first SoC, sama7g5.

Signed-off-by: Eugen Hristev <eugen.hristev@microchip.com>
[claudiu.beznea@microchip.com: keep only the sama7_dt]
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210415105010.569620-23-claudiu.beznea@microchip.com