sepolicy[1/8]: start MintKatROM common sepolicy

Rather than having to maintain out of tree changes, it is often
easier to maintain a hiearchy of changes, starting with the vendors
common config file. From there, inheriting products can pick up a base
and start to add or remove certain bits from it, making use of the
BOARD_SEPOLICY_* functions documented in external/sepolicy/README.

It requires: https://gerrit.omnirom.org/#/c/4795/

**Thanks Omni
Signed-off-by: Humberto Borba <humberos@gmail.com>
Signed-off-by: William Roberts<wroberts@tresys.com>
Change-Id: I13244e5c6fc64ef5c3f94ff2bc03fcbc96619490