usb: usb251xb: add boost-up property support

Add support for boost-up register of usb251xb hub.
boost-up property control USB electrical drive strength
This register can be set:

- Normal mode -> 0x00
- Low -> 0x01
- Medium -> 0x10
- High -> 0x11

(Normal Default)

References:
- http://www.mouser.com/catalog/specsheets/2514.pdf p29

Reviewed-by: Richard Leitner <[e-mail]>
Signed-off-by: Tommaso Merciai <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/misc/usb251xb.c

···
 	if (of_property_read_u16_array(np, "language-id", &hub->lang_id, 1))
 		hub->lang_id = USB251XB_DEF_LANGUAGE_ID;
 
+	if (of_property_read_u8(np, "boost-up", &hub->boost_up))
+		hub->boost_up = USB251XB_DEF_BOOST_UP;
+
 	cproperty_char = of_get_property(np, "manufacturer", NULL);
 	strlcpy(str, cproperty_char ? : USB251XB_DEF_MANUFACTURER_STRING,
 		sizeof(str));
···
 	 * may be as soon as needed.
 	 */
 	hub->bat_charge_en = USB251XB_DEF_BATTERY_CHARGING_ENABLE;
-	hub->boost_up = USB251XB_DEF_BOOST_UP;
 	hub->boost_57 = USB251XB_DEF_BOOST_57;
 	hub->boost_14 = USB251XB_DEF_BOOST_14;
 	hub->port_map12 = USB251XB_DEF_PORT_MAP_12;