Convert CONFIG_HAS_FSL_DR_USB to Kconfig

This converts the following to Kconfig:
   CONFIG_HAS_FSL_DR_USB

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/freescale/common/Kconfig b/board/freescale/common/Kconfig
index b0e6e43..195fc47 100644
--- a/board/freescale/common/Kconfig
+++ b/board/freescale/common/Kconfig
@@ -108,3 +108,7 @@
 	bool "Access to QIXIS is over i2c"
 	depends on FSL_QIXIS
 	default y
+
+config HAS_FSL_DR_USB
+	def_bool y
+	depends on USB_EHCI_HCD && PPC