R600: Promote i64 stores to v2i32

Now we need only one 64-bit pattern for stores.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211643 91177308-0d34-0410-b5e6-96231b3b80d8
R600/SI: Use a ComplexPattern for MUBUF stores

Now that non-leaf ComplexPatterns are allowed we can fold all the MUBUF
store patterns into the instruction definition.  We will also be able to
reuse this new ComplexPattern for MUBUF loads and atomic operations.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@211644 91177308-0d34-0410-b5e6-96231b3b80d8