SELinux changes for Treble Loadable Kernel Module

This change extends the recovery mode modprobe sepolicy
to support loadable kernel module in normal mode by using
statement below in init.rc:

exec u:r:modprobe:s0 -- /system/bin/modprobe \
    -d /vendor/lib/modules mod

Bug: b/35653245
Test: sailfish  with local built kernel and LKM enabled
Change-Id: I827e2ce387c899db3e0e179da92e79c75d61f5ae
(cherry picked from commit b638d949)