eglfs: prevent expose/geometrychange loop

This prevents EGLFS from getting stuck after
exposing the first frame, by constantly generating
new Expose and GeometryChange events which are
synchronously processed.

Change-Id: Id3b09821ea31e9c1ddab7c520e782a4e42844a08
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
eglfs: Fix bug determining physical screen size

In the situation that the screenSize EGLFS hook had been defined, but
not the physicalScreenSize, the uninitialized contents of
fb_var_screeninfo vinfo would be used to calculate the fall-back
physical screen size.  Since this value is undefined, devices like the
Raspberry Pi would end unable to render DPI dependent fonts.

Change-Id: Ic9f67c1c646cc7b328b695b76a84d78577fefcd8
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>