logos: add Toradex logo

Use the boot loader splash screen from WinCE which matches our
wallpapers position wise. Although the logo is an 8-bit indexed BMP as
well colours looked odd at first in U-Boot. After converting to full
RGB palette and converting back to an indexed BMP using imagemagick
the Logo showed up properly.

$ convert tools/logos/toradex-rgb.bmp -type Palette -colors 256 \
-compress none -verbose BMP3:tools/logos/toradex.bmp

Signed-off-by: Stefan Agner <stefan.agner@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>