defconfig: branding

As well as make it proper so it gives good and working builds
Change-Id: I008962c164a408295d9a0df7090590010b1b9779
defconfig: Revert to GZIP compression

XZ offers no advantages. With proper dtb inline build, zImages size is
now absolutely normal.

Change-Id: I88fefcdb413fc9b5922e5a515a928fa3bee18ae9