Fix N32 registers and stack alignment.

This patch fixes the "n" and "S" components of the data layout for mips. Clang
already gets this right.

This will be tested in clang.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@197536 91177308-0d34-0410-b5e6-96231b3b80d8