Tested on a maguro variant.

Change-Id: I99085d575e3d884fb04ac03ac998eb3c53eb2d9f

Change-Id: I22f49db3d59b50ed8975d8c1146bb9c322adbf7e

Only label properties with the ril. prefix with rild_prop.
Allow rild and system (and radio) to set radio_prop.
Only rild can set rild_prop presently.

New property_contexts file for property selabel backend.
New property.te file with property type declarations.
New property_service security class and set permission.
Allow rules for setting properties.

Avoid any future collisions with the use of .fc or .te suffixes in the
per-device directories.  If we want multiple file support, add a separate
subdirectory for sepolicy files.

Allow reading of properties area, which is now created before init has switched contexts.  Revisit this later - we should explicitly label the properties file.