Allow shell serial_device read-write access

When starting the emulator, the system console writes entries
to /dev/ttyS2. We need to allow the writes, otherwise this generates
denials when you run "emulator -verbose -logcat '*:v' -show-kernel"

Addresses the following denial:
type=1400 audit(1395076594.320:446): avc:  denied  { read write } for  pid=5600 comm="sh" path="/dev/ttyS2" dev="tmpfs" ino=1487 scontext=u:r:shell:s0 tcontext=u:object_r:serial_device:s0 tclass=chr_file

Bug: 13506702
Change-Id: I3729537cabb0bf8e8b2905d3def43a293bb1081f
diff --git a/target/board/generic_mips/BoardConfig.mk b/target/board/generic_mips/BoardConfig.mk
index 85bf7d7..6d222e6 100644
--- a/target/board/generic_mips/BoardConfig.mk
+++ b/target/board/generic_mips/BoardConfig.mk
@@ -68,5 +68,6 @@
         mediaserver.te \
         qemud.te \
         rild.te \
+        shell.te \
         surfaceflinger.te \
         system_server.te