Allow system settings to read /proc/version

Used to display kernel version in settings app.

avc: denied { read } for name="version" dev="proc"
scontext=u:r:system_app:s0 tcontext=u:object_r:proc_version:s0
tclass=file permissive=0

Bug: 66985744
Test: kernel version now displayed in settings app.
Change-Id: I53f92f63362b900347fd393a40d70ccf5d220d30