[ARM] Fix Neon vector type alignment to 64-bit

The maximum alignment for ARM NEON data types should be 64-bits as specified
in ARM procedure call standard document Sec. A.2 Notes.
This patch fixes it from its current larger natural default values, except
for Android (so as not to break existing ABI).
Reviewed by: Stephen Hines, Renato Golin.
Differential Revision: https://reviews.llvm.org/D33205

llvm-svn: 304201