[llvm][CodeGen] Addressing modes for SVE stN.

This reverts commit 17b1869b.

It is an attempt to fix the failure reported at

The patch differs from the original one reviwed at
https://reviews.llvm.org/D77435 only for the use of the std::make_tuple
in building the return value of `findAddrModeSVELoadStore`:

   -  return {IsRegReg ? Opc_rr : Opc_ri, NewBase, NewOffset};
   +  return std::make_tuple(IsRegReg ? Opc_rr : Opc_ri, NewBase,

the original patch submitted at
https://github.com/llvm/llvm-project/commit/fc4e954ed5c0825cdfe3a590ff1904ef38bc47db
was failing the following build:

http://lab.llvm.org:8011/builders/clang-armv7-linux-build-cache/builds/29420/

with error:

/home/buildslave/buildslave/clang-armv7-linux-build-cache/llvm/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp
/home/buildslave/buildslave/clang-armv7-linux-build-cache/llvm/llvm/lib/Target/AArch64/AArch64ISelDAGToDAG.cpp:1439:10:
error: chosen constructor is explicit in copy-initialization
  return {IsRegReg ? Opc_rr : Opc_ri, NewBase, NewOffset};
           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   /usr/bin/../lib/gcc/arm-linux-gnueabihf/5.4.0/../../../../include/c++/5.4.0/tuple:479:19:
   note: explicit constructor declared here
           constexpr tuple(_UElements&&... __elements)
	                     ^
			     1 error generated.