sunxi: change target to use FIT kernel images

sunxi: change target to use FIT kernel images

Modernize the target slightly to use kernel+dtb FIT images in all
subtargets. LZMA compression will be used for the cortexa53 devices,
and we'll stay conservative and use gzip for the cortexa7/a8 devices
due to performance differences.

Tested-on:
 - Linksprite pcDuino v2 (cortexa8 / A10)
 - Olinuxino Micro (cortexa7 / A20)
 - Banana Pi M2 Berry (cortexa7 / V40)
 - Banana Pi P2 Zero (cortexa7 / H2+)
 - Xunlong Orange Pi 2 (cortexa7/ H3)
 - OrangePi PC Zero 2 (cortexa53 / H616)

Signed-off-by: Zoltan HERPAI <[email protected]>