extcon: Move OF helper function to extcon core and change function name

This patch move simply OF helper function to extcon core and change function
name as following:
- of_extcon_get_extcon_dev() -> extcon_get_edev_by_phandle()

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>
Acked-by: Felipe Balbi <balbi@ti.com>
diff --git a/drivers/usb/dwc3/dwc3-omap.c b/drivers/usb/dwc3/dwc3-omap.c
index b269dbd..b1d7ee6 100644
--- a/drivers/usb/dwc3/dwc3-omap.c
+++ b/drivers/usb/dwc3/dwc3-omap.c
@@ -29,7 +29,6 @@
 #include <linux/of.h>
 #include <linux/of_platform.h>
 #include <linux/extcon.h>
-#include <linux/extcon/of_extcon.h>
 #include <linux/regulator/consumer.h>
 
 #include <linux/usb/otg.h>
@@ -522,7 +521,7 @@
 	dwc3_omap_enable_irqs(omap);
 
 	if (of_property_read_bool(node, "extcon")) {
-		edev = of_extcon_get_extcon_dev(dev, 0);
+		edev = extcon_get_edev_by_phandle(dev, 0);
 		if (IS_ERR(edev)) {
 			dev_vdbg(dev, "couldn't get extcon device\n");
 			ret = -EPROBE_DEFER;