[NVPTX][NFC] Use same logic to get alignment in param declarations and function prototypes (#98220)

Unifies the logic used to choose function prototype argument alignment
and param alignment declared in the caller. The call in `getPrototype`
to `getAlign`/`getFunctionParamOptimizedAlign` is replaced with
`getArgumentAlignment`, which is what is currently used to select the
alignment for the param declarations. This avoids code duplication of
`getAlign().value_or(getFunctionParamOptimizedAlign())` and ensures that
param alignments are the same in declarations and prototypes.

Author: kalxr

llvm/lib/Target/NVPTX/NVPTXISelLowering.cpp

@@ -1438,10 +1438,8 @@ std::string NVPTXTargetLowering::getPrototype(
 
     if (!Outs[OIdx].Flags.isByVal()) {
       if (IsTypePassedAsArray(Ty)) {
-        const CallInst *CallI = cast<CallInst>(&CB);
         Align ParamAlign =
-            getAlign(*CallI, i + AttributeList::FirstArgIndex)
-                .value_or(getFunctionParamOptimizedAlign(F, Ty, DL));
+            getArgumentAlignment(&CB, Ty, i + AttributeList::FirstArgIndex, DL);
         O << ".param .align " << ParamAlign.value() << " .b8 ";
         O << "_";
         O << "[" << DL.getTypeAllocSize(Ty) << "]";