telephony: Use reflection to create command interface (RIL class)

This has the advantage over the method used in CM7 in that the
RIL class for each device does not have to be specified in this
file in an if statement. ro.telephony.ril_class needs to be upated
to contain the name of the class instead of an identifier as used
in CM7

Change-Id: I0aafdfc78d47f493a2e35819dbe873ea98787934