km/scripts: load fdt_bid_kwkey.dtb when working with tftp

km/scripts: load fdt_bid_kwkey.dtb when working with tftp

When loading the dtb file via tftp we should load the one which matches
boardId and hwKey and not a common one for the boardname. We have boards
were different hwKeys are used and then we may load an incorrect dtb
file. If no fdt_bid_kwkey.dtb file is not a fallback to boardname.dtb is used.

Signed-off-by: Holger Brunck <holger.brunck@keymile.com>
Signed-off-by: Tobias Müller <Tobias.Mueller@keymile.com>
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Reviewed-by: Heiko Schocher <hs@denx.de>