configs: pandaboard: bump u-boot to 2015.10 and kernel to 4.3

VFPv3 and NEON was enabled and a readme.txt file was added.

Fixes bug #7580.

Tested on Pandaboard ES.

[Peter: use EABIhf]
Signed-off-by: Sergio Prado <sergio.prado@e-labworks.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>