Replace TSFlagsFields and TSFlagsShifts with a simpler TSFlags field.

When a target instruction wants to set target-specific flags, it should simply
set bits in the TSFlags bit vector defined in the Instruction TableGen class.

This works well because TableGen resolves member references late:

class I : Instruction {
  AddrMode AM = AddrModeNone;
  let TSFlags{3-0} = AM.Value;
}

let AM = AddrMode4 in
def ADD : I;

TSFlags gets the expected bits from AddrMode4 in this example.

llvm-svn: 100384