arm64: dts: colibri-imx8x: enable dtbs build

Commit d1825330 ("LF-10676-5 arm64: dts: imx: fix graph_child_address build warnings")
commented out colibri imx8x device trees from Makefile.
Re-enable the colibri dtbs build.

This commit fixes a NXP downstream specific commit.

Upstream-Status: Inappropriate [other]
Signed-off-by: Emanuele Ghidoli <emanuele.ghidoli@toradex.com>