Revert "Revert "Stk is already inherited from vendor/cm/config/gsm.mk""

Add the stk to the actual CDMA/LTE device repos, not globally (it is not
going to be used for CDMA build for Photon Q).
This reverts commit 5b2716ade1cce1f1780cd795d0c99cb1e4e292d2.
Remove ro.product.model.exif (leftover from stock firmware)

Additonally it's device specific.