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/usbarmory_defconfig b/configs/usbarmory_defconfig
index b1f8724..46f9996 100644
--- a/configs/usbarmory_defconfig
+++ b/configs/usbarmory_defconfig
@@ -15,4 +15,5 @@
 CONFIG_ENV_IS_IN_MMC=y
 CONFIG_FSL_ESDHC=y
 CONFIG_USB=y
+CONFIG_USB_EHCI_MX5=y
 CONFIG_OF_LIBFDT=y