Major changes to Thumb (not Thumb2). Many 16-bit instructions either modifies CPSR...

Major changes to Thumb (not Thumb2). Many 16-bit instructions either modifies CPSR  when they are outside the IT blocks, or they can predicated when in Thumb2. Move the implicit def of CPSR to an optional def which defaults CPSR. This allows the 's' bit to be toggled dynamically.

A side-effect of this change is asm printer is now using unified assembly. There are some minor clean ups and fixes as well.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@75359 91177308-0d34-0410-b5e6-96231b3b80d8