weston.ini: Fix weston.ini selection and postinstall for rotation and platform

The buildsystem took the wrong weston.ini for tanaro, move it the machine and imx subfolder (freescales override has higher prio).

Fix the access to the gfplatdetect detect module, as not available on all platforms. Use soc0/machine has fallback.

Set the rotation only if the fbcon path is found, to not fail on devices without display.