Simplify printing of ARM shifted immediates.

Simplify printing of ARM shifted immediates.

Print shifted immediate values directly rather than as a payload+shifter
value pair. This makes for more readable output assembly code, simplifies
the instruction printer, and is consistent with how Thumb immediates are
 displayed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134902 91177308-0d34-0410-b5e6-96231b3b80d8