R600: Move MIN/MAX matching from LowerOperation() to PerformDAGCombine()
R600: Expand i64 SELECT_CC
R600/SI: Fix SMRD pattern for offsets > 32 bits

We were dropping the high bits of 64-bit immediate offsets.
R600/SI: Teach SIInstrInfo::moveToVALU() how to move S_LOAD_*_IMM instructions