Add odm sepolicy support to SELinuxMMAC.java

Currently there are two mac permission files:
    - /system/etc/selinux/plat_mac_permissions.xml
    - /vendor/etc/selinux/nonplat_mac_permissions.xml

The change renames nonplat_mac_permissions.xml to
vendor_mac_permissions.xml.
It also adds odm_mac_permissions.xml but allows it to be optional:
    - /system/etc/selinux/plat_mac_permissions.xml
    - /vendor/etc/selinux/vendor_mac_permissions.xml
    - /odm/etc/selinux/odm_mac_permissions.xml (optional)

Also cleans up comments to reflect the change.

Bug: 64240127
Test: boot sailfish normally without odm
Test: boot another device having odm
Change-Id: I87d01215a65e75bf33659ed03797ffda5393d5a4