MIPS: Declare MSA MI10 instruction formats

Declare a struct describing the MSA MI10 instruction format used for ld &
st instructions, for use by subsequent patches.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-kernel@vger.kernel.org
Cc: Markos Chandras <markos.chandras@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/10571/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>