keymile, 8321 boards: move common definitions to km8321-common.h

First step for a cleanup of all header files for km8321 boards.

Signed-off-by: Thomas Reufer <thomas.reufer@keymile.com>
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>
cc: Heiko Schocher <hs@denx.de>