[SelectionDAGBuilder] Use ::precise LocationSizes; NFC

More migration so we can disable the implicit int -> LocationSize
conversion.

All of these are either scatter/gather'ed vector instructions, or direct
loads. Hence, they're all precise.

Perhaps if we see way more getTypeStoreSize calls, we can make a
getTypeStoreLocationSize (or similar) as a wrapper that applies this
::precise. Doesn't appear that it's a good idea to make getTypeStoreSize
return a LocationSize itself, however.

llvm-svn: 350042