Fix mapping of @llvm.arm.ssat/usat intrinsics to ssat/usat instructions for Thumb2

Summary:
r250697 fixed the mapping for ARM mode. We have to do the same for Thumb2 otherwise the same llvm.arm.ssat() will generate different saturating amount for ARM and Thumb.

r250697: http://reviews.llvm.org/rL250697

Reviewers: rmaprath

Subscribers: aemerson, llvm-commits, rengolin

Differential Revision: http://reviews.llvm.org/D15653

llvm-svn: 256115