[Autobackout][FuncReg]Revert of change: b533cc9

 Turn on LdStCombine

Turn LdStCombine on (for store only for now), which is on only for OCL path.
For now, limit platforms that have LSC msg; will enable legacy message later.

Author: jgu222

IGC/common/igc_flags.h

@@ -408,7 +408,7 @@ DECLARE_IGC_REGKEY(bool, DisableGPGPUIndirectPayload,   false, "Disable OCL indi
 DECLARE_IGC_REGKEY(bool, DisableDSDualPatch,            false, "Setting it to true with enable Single and Dual Patch dispatch mode for Domain Shader", false)
 DECLARE_IGC_REGKEY(bool, DisableMemOpt,                 false, "Disable MemOpt, merging load/store", false)
 DECLARE_IGC_REGKEY(bool, DisableMemOpt2,                false, "Disable MemOpt2", false)
-DECLARE_IGC_REGKEY(DWORD, EnableLdStCombine,            1,     "Enable load/store combine pass if set to 1 or 2 (intend to replace memopt)", true)
+DECLARE_IGC_REGKEY(DWORD, EnableLdStCombine,            0,     "Enable load/store combine pass if set to 1 or 2 (intend to replace memopt)", true)
 DECLARE_IGC_REGKEY(DWORD, MaxStoreVectorSizeInBytes,    0,     "[LdStCombine] the max non-uniform vector size for the coalesced store. 0: compiler choice (default, 16(4DW)); others: 8/16/32", true)
 DECLARE_IGC_REGKEY(DWORD, MaxLoadVectorSizeInBytes,     0,     "[LdStCombine] the max non-uniform vector size for the coalesced load.  0: compiler choice (default, 16(4DW)); others: 8/16/32", true)
 DECLARE_IGC_REGKEY(DWORD,MaxLiveOutThreshold,           0,     "Max LiveOut Threshold in MemOpt2", false)