dt-bindings: mfd: Document syscons falling back to atmel,sama5d2-sfrbu

dt-bindings: mfd: Document syscons falling back to atmel,sama5d2-sfrbu

The sfrbu on both sama7g5 and sama6d65 both fall back to sama5d2 in
devicetrees, but the former two compatibles were undocumented. Now that
syscon.yaml has easy support for multiple soc-specific compatibles, add
both of these undocumented devices.

Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Link: https://patch.msgid.link/20251117-marlin-mustang-5ffda4d211c7@spud
Signed-off-by: Lee Jones <lee@kernel.org>