Modified the linux sources to point at digilents git repo, master-next branch.

By the time of this commit, using the targets u-boot-digilent and linux-digilent it is possible to build the bootloader and kernel.

Ie,
bitbake -f -c compile u-boot-digilent
bitbake -f -c compile linux-digilent

Sign off: Rikard Söderström <soderstrom.rikard@gmail.com>