config: Add 'make kvmconfig'

config: Add 'make kvmconfig'

This patch adds 'make kvmconfig' which allows to add KVM guest support
to a config file.

This allows for easier testing of configurations under virtualized
environments.

Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: <linux-kbuild@vger.kernel.org>
Cc: <linux-kernel@vger.kernel.org>
Acked-by: Ingo Molnar <mingo@elte.hu>
Acked-by: Michal Marek <mmarek@suse.cz>
Suggested-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>