powerpc/512x: silence a USB Kconfig dependency warning

the PPC_MPC512x config automatically selected USB_EHCI_BIG_ENDIAN_*
switches, which made Kconfig warn about "unmet direct dependencies":

  scripts/kconfig/conf --silentoldconfig Kconfig
  warning: (PPC_MPC512x && 440EPX) selects USB_EHCI_BIG_ENDIAN_DESC which has unmet direct dependencies (USB_SUPPORT && USB && USB_EHCI_HCD)
  warning: (PPC_MPC512x && PPC_PS3 && PPC_CELLEB && 440EPX) selects USB_EHCI_BIG_ENDIAN_MMIO which has unmet direct dependencies (USB_SUPPORT && USB && USB_EHCI_HCD)
  warning: (PPC_MPC512x && 440EPX) selects USB_EHCI_BIG_ENDIAN_DESC which has unmet direct dependencies (USB_SUPPORT && USB && USB_EHCI_HCD)
  warning: (PPC_MPC512x && PPC_PS3 && PPC_CELLEB && 440EPX) selects USB_EHCI_BIG_ENDIAN_MMIO which has unmet direct dependencies (USB_SUPPORT && USB && USB_EHCI_HCD)

make the selected entries additionally depend on USB_EHCI_HCD which
silences the warning
Signed-off-by: NGerhard Sittig <gsi@denx.de>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/512x/Kconfig

@@ -7,8 +7,8 @@ config PPC_MPC512x
 	select PPC_PCI_CHOICE
 	select FSL_PCI if PCI
 	select ARCH_WANT_OPTIONAL_GPIOLIB
-	select USB_EHCI_BIG_ENDIAN_MMIO
-	select USB_EHCI_BIG_ENDIAN_DESC
+	select USB_EHCI_BIG_ENDIAN_MMIO if USB_EHCI_HCD
+	select USB_EHCI_BIG_ENDIAN_DESC if USB_EHCI_HCD
 
 config MPC5121_ADS
 	bool "Freescale MPC5121E ADS"