keymile boards: move keymile specific header in subdir

Collect all keymile specific common headers in include/configs/km.

Signed-off-by: Heiko Schocher <hs@denx.de>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Wolfgang Denk <wd@denx.de>
cc: Detlev Zundel <dzu@denx.de>
cc: Prafulla Wadaskar <prafulla@marvell.com>
cc: Kim Phillips <kim.phillips@freescale.com>
cc: Holger Brunck <holger.brunck@keymile.com>