kernel: enable debug info for all builds

We do this for many configs already (either via defconfig or via some of
the kconf fragments), so move it to the common default for everyone.  It
helps with debugging w/out affecting runtime behavior (it does increase
the build time a bit, but should be negligible).

Change-Id: Ia80b15acd9161eb59fa85713e663f29ad65d7b79
3 files changed