kvm tools: Add 'install' target to Makefile

kvm tools: Add 'install' target to Makefile

Add a new 'install' target to Makefile that installs 'lkvm' binary to
$HOME/bin by default. The installed binary still needs to be launched
from linux/tools/kvm directory because of our silly external dependency
to stage 2 guest init file:

  [penberg@tux ~]$ lkvm run
    Fatal: Failed linking stage 2 of init.

The most convinent way to fix that is to embed the stage 2 image in
'lkvm' executable like we do with our mini-BIOS.

Signed-off-by: Pekka Enberg <penberg@kernel.org>