arm/km: enable FDT for km_kirwkood

This consists of:
a) Defining the addresses, enabling fdtsupport [arm]
b) Defining "cramfsloadfdt"  [arm,powerpc => common]
c) Adding the FDT address to bootm [arm,powerpc => common]
d) Defining "tftpfdt" in ramfs-,develop- [arm,powerpc >= common]

This should work with 3.10 kernels, whether loaded through TFTP
(with rootfs either through NFS or TFTP-ramfs) or from the NAND.

The machid was left unchanged, this should keep compatibility with both
older and newer kernels.

Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Signed-off-by: Gerlando Falauto <gerlando.falauto@keymile.com>
Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Acked-by: Valentin Longchamp <valentin.longchamp@keymile.com>