Allow TCGETS on pipes (fifo_file)

Allow a process to determine if a fifo_file (aka pipe, created from the
pipe() or pipe2() syscall) is a tty.

Addresses the following denials:

type=1400 audit(0.0:1307): avc: denied { ioctl } for comm="ls" path="pipe:[213117]" dev="pipefs" ino=213117 ioctlcmd=5401 scontext=u:r:hal_dumpstate_impl:s0 tcontext=u:r:hal_dumpstate_impl:s0 tclass=fifo_file permissive=0
type=1400 audit(0.0:22): avc: denied { ioctl } for comm="sh" path="pipe:[54971]" dev="pipefs" ino=54971 ioctlcmd=5401 scontext=u:r:untrusted_app_27:s0:c512,c768 tcontext=u:r:untrusted_app_27:s0:c512,c768 tclass=fifo_file permissive=0 app=com.zhihu.android
type=1400 audit(0.0:237): avc: denied { ioctl } for comm="sh" path="pipe:[56997]" dev="pipefs" ino=56997 ioctlcmd=5401 scontext=u:r:untrusted_app_25:s0:c512,c768 tcontext=u:r:untrusted_app_25:s0:c512,c768 tclass=fifo_file permissive=0 app=fm.qingting.qtradio

Test: policy compiles and device builds.
Change-Id: Ic4c6441d0ec33de8cda3f13ff529e98374897364