ixp4xx.inc: prefer tar.xz or tar.gz images

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
linux-ixp4xx 2.6.37: make EHCI a builtin

No noticable size difference, but it makes testing kernels a lot easier.

Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>
Merge pull request #5 from koenkooi/master

2 tweaks