[ARM] MV78xx0: Support for Buffalo WXL (Terastation Duo)

* Modification of Kconfig to add the Option
* 1 new file : buffalo-wxl-setup.c
This file is inspired from the db-78xx0-setup.c already present.
The following is done:
  - Configure MPP Lines for the plateform (see my patch for MPP)
This is taken from the stock kernel provided by buffalotech (the vendor)
  - GigaBit Ethernet
  - Sata
  - Uart are initiallized in a different way than on the dev board as we
have one core only.
  - USB

The kernel has been running for some days now on my plateform.

Signed-off-by: Sebastien Requiem <sebastien@kolios.dk>
Signed-off-by: Nicolas Pitre <nico@marvell.com>