dm: device: make power domain calls optional

Reduce power domain calls when CONFIG_POWER_DOMAIN is disabled.
With gcc v8.2, this change saves 104 bytes.

Signed-off-by: Anatolij Gustschin <agust@denx.de>
Reviewed-by: Peng Fan <peng.fan@nxp.com>
diff --git a/drivers/core/device.c b/drivers/core/device.c
index 37d89bc..474c164 100644
--- a/drivers/core/device.c
+++ b/drivers/core/device.c
@@ -388,7 +388,8 @@
 	if (dev->parent && device_get_uclass_id(dev) != UCLASS_PINCTRL)
 		pinctrl_select_state(dev, "default");
 
-	if (dev->parent && device_get_uclass_id(dev) != UCLASS_POWER_DOMAIN) {
+	if (CONFIG_IS_ENABLED(POWER_DOMAIN) && dev->parent &&
+	    device_get_uclass_id(dev) != UCLASS_POWER_DOMAIN) {
 		if (!power_domain_get(dev, &pd))
 			power_domain_on(&pd);
 	}