The LLVM and GCC teams agreed to rename the __builtin_mma_assemble_pair and
__builtin_mma_disassemble_pair built-ins to __builtin_vsx_assemble_pair and
__builtin_vsx_disassemble_pair respectively. This patch is to make
corresponding changes in dgemm kernel. Also made changes in
inputs to those builtins to avoid some potential typecasting issues.
Reference gcc commit id:77ef995c1fbcab76a2a69b9f4700bcfd005d8e62
0571c3187b