power: reset: syscon-reboot: Add parental syscon support

Since normally syscon-reboot block is supposed to be a part of a system
controller, lets look for the syscon regmap in a parental DT node if
regmap property isn't specified. DT binding from now considers the regmap
property as deprecated.

Signed-off-by: Serge Semin <[e-mail]>
Cc: Alexey Malahov <[e-mail]>
Cc: Thomas Bogendoerfer <[e-mail]>
Signed-off-by: Sebastian Reichel <[e-mail]>

drivers/power/reset/syscon-reboot.c

···
 		return -ENOMEM;
 
 	ctx->map = syscon_regmap_lookup_by_phandle(dev->of_node, "regmap");
-	if (IS_ERR(ctx->map))
-		return PTR_ERR(ctx->map);
+	if (IS_ERR(ctx->map)) {
+		ctx->map = syscon_node_to_regmap(dev->parent->of_node);
+		if (IS_ERR(ctx->map))
+			return PTR_ERR(ctx->map);
+	}
 
 	if (of_property_read_u32(pdev->dev.of_node, "offset", &ctx->offset))
 		return -EINVAL;