memul: Add device specific policies

Change-Id: Ieb687bdaa13f7e6d15e43d87c39e49a2d9a9124e
memul: Mount firmware partitions with firmware_file context

* we don't need to give ueventd access across the entire vfat context

Change-Id: Idf1e24b7b90fd439d1d3ee2cd839c43078f026c7
memul: Add more SELinux policies

Change-Id: I17ab585c89fd17177e6319757dbc1030191a73a4