Removed SELECT_CC custom lowering. This is not needed anymore, the SELECT node

is lowered properly and covers everything LowerSELECT_CC did.
Added method printUnsignedImm in AsmPrinter to print uimm16 operands. This
avoid the ugly instruction by instruction checking in printOperand.
Added a swap instruction present in the allegrex core.
Added two conditional instructions present in the allegrex core : MOVZ and MOVN.
They both allow a more efficient SELECT operation for integers.
Also added SELECT patterns to optimize MOVZ and MOVN usage.
The brcond and setcc patterns were cleaned: redundant and suboptimal patterns
were
removed. The suboptimals were replaced by more efficient ones.
Fixed some instructions that were using immZExt16 instead of immSExt16.

llvm-svn: 54724