sepolicy : sysmonappExternal permission for dsp_device

The permission to access the dsp_devices is for future,
it could be not apply until it is enabled by the
sysmonappExternal application.

Currently, the permission to access the xdsp_devices is
denied as:
I auditd  : type=1400 audit(0.0:838): avc: denied { read }
for comm="smonappExternal" name="adsprpc-smd-secure"
dev="tmpfs" ino=25601
scontext=u:r:sysmon_app:s0:c112,c256,c512,c768
tcontext=u:object_r:xdsp_device:s0 tclass=chr_file
permissive=0

W smonappExternal: type=1400 audit(0.0:838):
avc: denied { read } for name="adsprpc-smd-secure"
dev="tmpfs" ino=25601
scontext=u:r:sysmon_app:s0:c112,c256,c512,c768
tcontext=u:object_r:xdsp_device:s0 tclass=chr_file
permissive=0

Difference to the qdsp_device, but the xdsp_device is
allowed to be used by the set of the sysmonappExternal
related application only. So don't define that access
in the app.te like the qdsp_device.
Binding the qdsp_device with the xdsp_device as they are
similiar type to ease any further operate on that,
though this is not mandatory as there is already a rule
to allow the app_domain to access the qdsp_device has been
defined in the app.te.

CRs-Fixed: 2248438
Change-Id: I8692776e1496580b7d86cb3b271d216c1a3ac906