Make ARM and Thumb2 32-bit immediate materialization into a single 32-bit pseudo

Make ARM and Thumb2 32-bit immediate materialization into a single 32-bit pseudo
instruction. This makes it re-materializable.

Thumb2 will split it back out into two instructions so IT pass will generate the
right mask. Also, this expose opportunies to optimize the movw to a 16-bit move.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@82982 91177308-0d34-0410-b5e6-96231b3b80d8