kconfig: Add yes2modconfig and mod2yesconfig targets.

Since kernel configs provided by syzbot are close to "make allyesconfig",
it takes long time to rebuild. This is especially waste of time when we
need to rebuild for many times (e.g. doing manual printk() inspection,
bisect operations).

We can save time if we can exclude modules which are irrelevant to each
problem. But "make localmodconfig" cannot exclude modules which are built
into vmlinux because /sbin/lsmod output is used as the source of modules.

Therefore, this patch adds "make yes2modconfig" which converts from =y
to =m if possible. After confirming that the interested problem is still
reproducible, we can try "make localmodconfig" (and/or manually tune
based on "Modules linked in:" line) in order to exclude modules which are
irrelevant to the interested problem. While we are at it, this patch also
adds "make mod2yesconfig" which converts from =m to =y in case someone
wants to convert from =m to =y after "make localmodconfig".

Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>