powerpc/p1_p2_rdb_pc: Fix endian access issue on EHCI intinalization

This issue is exposed after commit 9000eddbae ("drivers/usb/ehci:
Use platform-specific accessors"), the wrong endianness of EHCI
controller programing will cause USB function down.

Signed-off-by: Ran Wang <ran.wang_1@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

include/configs/p1_p2_rdb_pc.h

@@ -782,6 +782,7 @@
 #ifdef CONFIG_USB_EHCI_HCD
 #define CONFIG_EHCI_HCD_INIT_AFTER_RESET
 #define CONFIG_USB_EHCI_FSL
+#define CONFIG_EHCI_DESC_BIG_ENDIAN
 #endif
 #endif