mediaserver needs the ability to read media_rw_data_file files.
Allow it. Similarly, this is also needed for drmserver. Addresses
the following denials:

<5>[   22.812859] type=1400 audit(1389041093.955:17): avc:  denied  { read } for  pid=1655 comm="MediaScannerSer" path="/data/media/0/DCIM/Camera/VID_20140106_124115.mp4" dev="mmcblk0p28" ino=122204 scontext=u:r:mediaserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file
<5>[   22.813103] type=1400 audit(1389041093.955:18): avc:  denied  { getattr } for  pid=849 comm="Binder_2" path="/data/media/0/DCIM/Camera/VID_20140106_124115.mp4" dev="mmcblk0p28" ino=122204 scontext=u:r:mediaserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file
<5>[   22.832041] type=1400 audit(1389041093.975:19): avc:  denied  { read } for  pid=849 comm="Binder_2" path="/data/media/0/DCIM/Camera/VID_20140106_124115.mp4" dev="mmcblk0p28" ino=122204 scontext=u:r:drmserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file
<5>[   52.357470] type=1400 audit(1389041123.494:29): avc:  denied  { read } for  pid=2757 comm="ImageLoader" path="/data/media/0/DCIM/Camera/VID_20140106_124520.mp4" dev="mmcblk0p28" ino=122211 scontext=u:r:mediaserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file
<5>[   52.357717] type=1400 audit(1389041123.494:30): avc:  denied  { getattr } for  pid=849 comm="Binder_2" path="/data/media/0/DCIM/Camera/VID_20140106_124520.mp4" dev="mmcblk0p28" ino=122211 scontext=u:r:mediaserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file
<5>[   52.382276] type=1400 audit(1389041123.524:31): avc:  denied  { read } for  pid=849 comm="Binder_2" path="/data/media/0/DCIM/Camera/VID_20140106_124520.mp4" dev="mmcblk0p28" ino=122211 scontext=u:r:drmserver:s0 tcontext=u:object_r:media_rw_data_file:s0 tclass=file

Allow anyone who has access to video_device:chr_file to also
have read access to video_device:dir. Otherwise, the
chracter devices may not be reachable.

Bug: 12416198
Change-Id: I649cd52ec7f1a25afb3aea479482e3f270bfe074