OpaquePtr: add Type parameter to Loads analysis API.

OpaquePtr: add Type parameter to Loads analysis API.

This makes the functions in Loads.h require a type to be specified
independently of the pointer Value so that when pointers have no structure
other than address-space, it can still do its job.

Most callers had an obvious memory operation handy to provide this type, but a
SROA and ArgumentPromotion were doing more complicated analysis. They get
updated to merge the properties of the various instructions they were
considering.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@365468 91177308-0d34-0410-b5e6-96231b3b80d8