powerpc, 83xx: add kmsupx5 board support

The Keymile SUPx5 board series is based on a PBEC8321 but
contains an additional PBUS FPGA (LPXF) on local bus CS2.

Signed-off-by: Thomas Reufer <thomas.reufer@keymile.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
Acked-by: Kim Phillips <kim.phillips@freescale.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Kim Phillips <kim.phillips@freescale.com>
cc: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Holger Brunck <holger.brunck@keymile.com>