Code was salvaged from !306

When MC for luma only is desired, use existing luma/chroma parameters
instead of encoder-specific field in data structure

Also take care that luma only MC doesn't imply IBC

Deleted the TU retrieval from the DQP code in xCompressCU and the TU pointer being equal to nullptr check.

Dereferencing a nullptr should be avoided, even if the passed object is never used.
It may not be the most elegant solution to pass an empty list object, but it should work.

IBC block search history status is not reset for each frame, which may affect IBC searching results for the second frame.