thermal: register thermal zone even if ref-channel not provided in DT

thermal: register thermal zone even if ref-channel not provided in DT

Register thermal zone even if ref-channel not provided in DT.
For Hawkeye platform SW need to read two channels to get system
temperature and battery temperature so need to provide ref-channel and
sensor-channel in DT, for all other platforms ref-channel not provided
in DT.

Bug 200083122

Change-Id: I30e618b0714c4c6d692345e36581f98259dda2fa
Signed-off-by: Venkat Reddy Talla <vreddytalla@nvidia.com>
Reviewed-on: http://git-master/r/724137
Reviewed-by: Laxman Dewangan <ldewangan@nvidia.com>