omap3evm: Wrap function under CONFIG_USB_OMAP3

The function omap3_evm_need_extvbus() is required
only when USB support is configured.

Wrapped this function in #ifdef CONFIG_USB_OMAP3.
Signed-off-by: NSanjeev Premi <premi@ti.com>
Signed-off-by: NSandeep Paulraj <s-paulraj@ti.com>

board/ti/evm/evm.c

@@ -64,6 +64,7 @@ static void omap3_evm_get_revision(void)
        }
 }
 
+#ifdef CONFIG_USB_OMAP3
 /*
  * MUSB port on OMAP3EVM Rev >= E requires extvbus programming.
  */
@@ -76,6 +77,7 @@ u8 omap3_evm_need_extvbus(void)
 
 	return retval;
 }
+#endif
 
 /*
  * Routine: board_init