[ARM][AsmParser] Improve debug printing of parsed asm operands

In ARMOperand::print:
- Print human-readable register names, instead of numbers.
- Print the correct names for IT condition masks (these were in the wrong order
  before).
- Print all parts of memory operands, not just the base register.

This makes the output of llvm-mc -show-inst-operands more readable.

Differential revision: https://reviews.llvm.org/D54850

llvm-svn: 347494