ScopInfo: Introduce ArrayKind

Since 252422 we do not only distinguish two ScopArrayInfo kinds, PHI nodes
and others, but work with three kind of ScopArrayInfo objects. SCALAR, PHI and
ARRAY objects. Instead of keeping two boolean flags isPHI and isScalar and
wonder what an ScopArrayInfo object of kind (!isScalar && isPHI) is, we
list now explicitly the three different possible types of memory objects.

This change also allows us to remove the confusing nested pairs that have
been used in ArrayInfoMapTy.

llvm-svn: 252620