Arm64 defconfig-debug

[Qian Cai]

Hi there, some general debugging features like kmemleak, KASAN, lockdep,
UBSAN etc help fix many bugs like a microscope. On the other hand, those
features are scatter around and mixed up with more situational debugging
options making them difficult to consume properly.

Since I have been deal with those options on a daily basis for the last
a few years and accumulated the knowledge of their pros and cons, I am
thinking about to create an initial defconfig-debug available inside the
tree, so that it could amplify the general debugging/testing efforts for
arm64 across the broad.

The downside is that this might open a gate for other people to push yet
another subject-specific defconfig, but I don't see anything as
important as general debugging/testing at the moment. Then, there are
two defconfig need to be modified for some common changes, but I think
that is quite trivial to do. We could even create a simple script to
sync if that is not overkill.