We can build modules on the target, but not the kernel itself. The kernel source, tools and configuration should be available as part of the SDK and as a standalone package. When the SDK or this package is used, it should be possible to rebuild the running kernel on the target itself.
Bruce, assigning to you and for M1 as I believe this is part of your pending patch set.
This is at risk for M1, due to the kernel build optimizations taking longer than expected. I'll bump to M2 if it misses.
This is now in-tree, and works with the kernel-devsrc package.