Move sysfs_thermal to global policy and grant access.

sysfs_thermal nodes are common enough to warrant an entry in global
policy and the new HardwarePropertiesManagerService exists explicitly to
expose some of this information.

Address the following denials:
avc: denied { search } for name="thermal" dev="sysfs" ino=17509 scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs_thermal:s0 tclass=dir permissive=1
avc: denied { read } for name="temp" dev="sysfs" ino=17848 scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs_thermal:s0 tclass=file permissive=1
avc: denied { open } for path="/sys/devices/virtual/thermal/thermal_zone8/temp" dev="sysfs" ino=17848 scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs_thermal:s0 tclass=file permissive=1
avc: denied { getattr } for path="/sys/devices/virtual/thermal/thermal_zone8/temp" dev="sysfs" ino=17848 scontext=u:r:system_server:s0 tcontext=u:object_r:sysfs_thermal:s0 tclass=file permissive=1

Bug: 27809332
Change-Id: I2dbc737971bf37d197adf0d5ff07cb611199300d