Change ARM data layout strings to match llvm-gcc.

Sandeep Patel noticed that the alignment was wrong for Neon vector types,
and this change is partly derived from his patch.  For the APCS ABI, however,
additional changes were required: the maximum ABI alignment is 32 bits and
the preferred alignment for i64 and f64 types should be 64 bits.

llvm-svn: 128825