MIPS: Remove unused defines in piix4.h

MIPS: Remove unused defines in piix4.h

The PIIX4_ICTLR* and PIIX4_OCW* defines are not used by any other files.
Remove them.

The only file (other than fixup-malta.c which includes piix4.h in patch #1)
containing "#include <asm/mips-boards/piix4.h>" is
arch/mips/mti-malta/malta-int.c whose first version is actually
"1da177e4c3:arch/mips/mips-boards/malta/malta_int.c". In that version, in
the function get_int(), things in piix4.h are used. But now malta-int.c no
longer needs those stuff.

Signed-off-by: Deng-Cheng Zhu <dengcheng.zhu@imgtec.com>
Cc: Steven J. Hill <Steven.Hill@imgtec.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6032/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>