Label /dev/goldfish_pipe as qemu_device

In goldfish kernel 3.10, qemu_pipe has been renamed to goldfish_pipe.
However, in the emulator's SELinux policy, there is no specific security
context assigned to /dev/goldfish_pipe, and the one inherited from /dev
(u:object_r:device:s0) prevents various processes (qemud, qemu-props,
etc.) from reading and writing goldfish_pipe. Consequently, the classic
x86_64 emulator will not boot if GPU emulation is enabled ("-gpu host"),
and does not render the UI correctly if launched with "-gpu off".

Fix this issue by assigning /dev/goldfish_pipe the same security context
as /dev/qemu_pipe.

This CL also benefits the new ("ranchu") emulator, where all supported
ABIs (arm64, mips64, x86 and x86_64) use 3.10-based kernels. Without
this fix, the new emulator boots and works, but there are avc denials
related to goldfish_pipe.

Last but not least, it is now possible to boot the classic x86 emulator
with a 3.10-based kernel instead of the current 3.4-based one, without
disabling SELinux.

(cherry-pick of commit: a5053e6b35)

Change-Id: I52e75c94d3ae3758cbbf5bc0e1d84254fdf5c6cb
Signed-off-by: Yu Ning <yu.ning@intel.com>

target/board/generic/sepolicy/file_contexts

@@ -1,6 +1,7 @@
 /dev/block/mtdblock0       u:object_r:system_block_device:s0
 /dev/block/mtdblock1       u:object_r:userdata_block_device:s0
 /dev/block/mtdblock2       u:object_r:cache_block_device:s0
+/dev/goldfish_pipe	u:object_r:qemu_device:s0
 /dev/qemu_.*		u:object_r:qemu_device:s0
 /dev/socket/qemud	u:object_r:qemud_socket:s0
 /system/bin/qemud	u:object_r:qemud_exec:s0