Add support for logging directly to RADIO LOG.

Eventually we will remove using the LOG_TAG in
system/core/liblog/logd_write.c to steer the log string
to the LOG_ID_RADIO buffer. This can't be done immediately
even if we changed all of the code in frameworks/opt/telephony
and frameworks/base/telephony because ril's and radio's are
relying on this behavior. But next year we will.

Change-Id: Ic36eaaca6f2a6302255e96a7646b687322d6997e