Ditch Kconfig and config.mk

[AkihiroSuda]

Personally I always thought that the kconfig mechanism is kind of weird.

I think at this point, the makefile targets could probably replace the Kconfig?

It's a bit doubled up, and having dedicated targets seemed to be preferred.

I mostly used it (as an alternative to autoconf), because I was familar with it...

Originally posted by @afbjorklund in #3321

[afbjorklund]

We use kconfig for Linux and Busybox, but it was probably overkill for Lima.