ARM: dts: at91: add Exegin Q5xR5 board

Add Exegin Q5xR5. The base device tree is from OpenWrt tree and with
the addition of this patch there will be no need to maintain it
separatelly in OpenWrt.

[osk: original author of patch in OpenWrt]
[claudiu.beznea: use "&<label> {" syntax, sorted nodes in alphabetical
 order, adapted flash to new support in kernel 5.14, use proper
 compatibles according to kernel 5.14, use macros instead of
 hardcoded numbers for pinctrl phandles and for all pinctrl references,
 add pinctrl-names, pinctrl-X where necessaray]

Signed-off-by: Owen Kirby <osk@exegin.com>
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210816064416.1630674-8-claudiu.beznea@microchip.com