lguest: select CONFIG_TTY to build properly.

Fix kconfig warning for LGUEST_GUEST config by selecting TTY:

warning: (KVMTOOL_TEST_ENABLE && LGUEST_GUEST) selects VIRTIO_CONSOLE which has unmet direct dependencies (VIRTIO && TTY)

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Joe Millenbach <jmillenbach@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>