mt6765-common: sepolicy: Allow system_app to access zram sysfs nodes

avc: denied { search } for name="zram0" dev="sysfs" ino=20744
scontext=u:r:system_app:s0 tcontext=u:object_r:sysfs_zram:s0 tclass=dir
permissive=0

avc: denied { open } for name="mem_used_total" dev="sysfs" ino=20804
scontext=u:r:system_app:s0 tcontext=u:object_r:sysfs_zram:s0 tclass=file
permissive=0

avc: denied { read } for name="mem_used_total" dev="sysfs" ino=20804
scontext=u:r:system_app:s0 tcontext=u:object_r:sysfs_zram:s0 tclass=file
permissive=0

Change-Id: Ide9b1a9488b26fa69e7a2c8e73a8e657c8b28beb