TEncSearch: use X265_MALLOC to allocate pixel buffers, and pixel type

--HG--
extra : rebase_source : d6c378452bc92841f56052cd6a50cbe8eeafd7b7
TEncSearch: use X265_MALLOC for UChar buffers, and uint8_t type

--HG--
extra : rebase_source : ab9b26448b6cbd8a81c8085f70cb222aff527512
TEncSearch: remove redundant m_hChromaShift, m_vChromaShift

TComPrediction has these members, and TEncSearch derives from TComPrediction

--HG--
extra : rebase_source : d24bfaa19fd67b55af1293b68bfded3a9bde83e1
TComYuv: combine copyPartToPartLuma and copyPartToPartChroma

The new function tries to ensure the proper chroma block is copied, when
necessary.