linux-user: Add support for more VT ioctls

DirectFB-1.0 uses at least two of the four added ioctls, and the two
others were added for completeness.  This patch was validated with the
program "vlock -all/-new".

Signed-off-by: Cédric VINCENT <cedric.vincent@st.com>
Cc: Riku Voipio <riku.voipio@iki.fi>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
