uboot-imx

travis-ci: Temporarily disable using a newer device tree compiler

For a long while dtc has warned about various constructs.  This is now
leading to log file size being exceeded in travis, and as the majority
of these errors need to be fixed in the kernel, switch to using the
stock device-tree-compiler package.

Signed-off-by: Tom Rini <trini@konsulko.com>