Remove uses of to-be-deprecated API. In cases where the correct
element type was not immediately obvious to me, fall back to
explicit getPointerElementType().
The main motivation behind pointer replacement of LDS use within non-kernel
functions is - to *avoid* subsequent LDS lowering pass from directly packing
LDS (assume large LDS) into a struct type which would otherwise cause allocating
huge memory for struct instance within every kernel.
Reviewed By: rampitec
Differential Revision: https://reviews.llvm.org/D103225