Tuner HAL VTS: Added LnbDescrambling

This CL implements a new dataflow: LnbDescrambling, which aims to test
descrambling a broadcast brought into the tuner with an Lnb attached.
The struct for the configuration and a function to read this dataflow
from the vendor's input file were added. Additionally, the api was
updated to allow the automatic xml parser to read this new dataflow.
Note, no tests were added for this object yet. Those come later in the
chain. The vendor, at this moment, can only harcode this dataflow. It
will be dynamically configurable later in the chain.

Bug: b/240476983

Test: ts-tradefed run vts --module VtsHalTvTunerTargetTest
Change-Id: I545be7d4b2bea0b80a67fd542a80bba7fa38c4ca