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

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

The mapping of these two intrinsics in ARMInstrInfo.td had a small
omission which lead to their operands not being validated/transformed
before being lowered into usat and ssat instructions. This can cause
incorrect instructions to be emitted.

I've also added tests for the remaining two saturating arithmatic
intrinsics @llvm.arm.qadd and @llvm.arm.qsub as they are missing
codegen tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@250697 91177308-0d34-0410-b5e6-96231b3b80d8