This is true, but we did get a patch from a community member to make it build, and I merged it.
There's a fairly good chance that this will work:

repo init -u git://android.git.linaro.org/platform/manifest.git -b linaro_android_4.2.2 --repo-url=http://android.git.linaro.org/git-ro/tools/repo -g common,arm,imx53,devel

repo sync

Or, if you're really brave, try

repo init -u git://android.git.linaro.org/platform/manifest.git -b linaro_android_4.3 --repo-url=http://android.git.linaro.org/git-ro/tools/repo -g common,arm,imx53,devel

repo sync

(We aren't doing any work on iMX53, but I don't see any changes between 4.2.2 and 4.3 that would break it or require porting kernel changes. If you submit any patches, we'll merge them, but we don't have the time to contribute beyond that. You may want to backport the ashmem kernel fixes from the 4.3 kernel releases for Galaxy Nexus, Nexus 4, Nexus 7 or Nexus 10.).