USB: remove USB_EHCI_BIG_ENDIAN_{DESC,MMIO} depends on architecture symbol

Just like the OHCI counter part we just can remove the architecture
specific symbols which prevent these configuration symbols from being
selected by platforms/architectures requiring it. The original
implementation did not scale at all since it required each and every
single architecture to be added for these configuration symbols to be
selected. Now it is up to the EHCI driver and/or platform to select
these configuration symbols accordingly.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>