Convert CONFIG_USB_EHCI_MX5 to Kconfig

This converts the following to Kconfig:
   CONFIG_USB_EHCI_MX5

Signed-off-by: Lukasz Majewski <lukma@denx.de>
diff --git a/configs/mx53ppd_defconfig b/configs/mx53ppd_defconfig
index 2a6183b..2379ab8 100644
--- a/configs/mx53ppd_defconfig
+++ b/configs/mx53ppd_defconfig
@@ -37,6 +37,7 @@
 CONFIG_MII=y
 CONFIG_RTC_S35392A=y
 CONFIG_USB=y
+CONFIG_USB_EHCI_MX5=y
 CONFIG_USB_STORAGE=y
 CONFIG_VIDEO=y
 CONFIG_VIDEO_IPUV3=y