Apply again changes to support ARM memory asm parsing. I removed

all LDR/STR changes and left them to a future patch. Passing all
checks now.

- Implement asm parsing support for LDRT, LDRBT, STRT, STRBT and
  fix the encoding wherever is possible.
- Add a new encoding bit to describe the index mode used and teach
  printAddrMode2Operand to check by the addressing mode which index
  mode to print.
- Testcases

llvm-svn: 128689