xserver-common: Rename Xsession.d files to end with .sh extension

* oe-core version of xinput-calibrator installs
  30xinput_calibrate.sh and ls -X used in Xsession script sorts it as
  last (not respecting the numbers) and xinput-calibrator is executed
  too late (after 90xXWindowManager)
* don't forget to update all your components installing Xsession.d
  files as well

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>