Don't hardcode fps for fake screen

Currently, when main hardware screen is powered-off,
X server initializes fake screen's timer with
1 second update interval.

Streaming software like Nomachine or Vnc, as well as
desktop input automation suffers from it, since it
will forever be stuck on 1 fps until the display is
turned back on.

This commit adds command line option -fakescreenfps <int>
that allows the user to change the default fake screen
timer.

Signed-off-by: Baranin Alexander <ismailsiege@gmail.com>
5 jobs for configurable_fake_interval in 5 minutes and 51 seconds (queued for 5 seconds)