buildroot

linux: Add new image formats for PowerPC and Microblaze

Add the following Linux kernel image formats:

 * cuImage(powerpc)
 * simpleImage(microblaze)
 * linux.bin(microblaze)

Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>