camera: allow loading files with text relocations from /system

the qcom camera driver needs to load a shared library from /system
which contains a text relocation. Allow it.

Due to bug 20013628, SELinux policy was inappropriately treating
an execmod denial as an execmem denial. Move to using a proper
execmod denial and get rid of execmem.

Addresses the following denial:
  avc: denied { execmod } for pid=387 comm="mm-qcamera-daem" path="/system/vendor/lib/libmmcamera_faceproc.so" dev="mmcblk0p41" ino=1871 scontext=u:r:camera:s0 tcontext=u:object_r:system_file:s0 tclass=file permissive=0

Bug: 20013628
Change-Id: I6611df77b9cbf2a78ed595d19fc80d63aa837183
diff --git a/sepolicy/camera.te b/sepolicy/camera.te
index 40e9c39..77cb8ef 100644
--- a/sepolicy/camera.te
+++ b/sepolicy/camera.te
@@ -5,7 +5,7 @@
 # Started by init
 init_daemon_domain(camera)
 
-allow camera self:process execmem;
+allow camera system_file:file execmod;
 
 # Interact with other media devices
 allow camera camera_device:dir search;