sepolicy: Move definitions from Android.mk to make opt-in

Move the BOARD definitions to sepolicy.mk to allow devices to opt
in rather then automatically include with Android.mk. Also include
lineage-specific qcom sepolicy now located in
device/lineage/sepolicy/qcom.

Original commits:
https://github.com/LineageOS/android_device_qcom_sepolicy/commit/959d3362451fe081d9a25fde87e989ffe90ab159
https://github.com/LineageOS/android_device_qcom_sepolicy/commit/27f078f1041497ecadf1315b39f130882177ea64

Change-Id: Ibf70e4c8ab9d91b50c62c3e9f1263e1624e8ca00