MIPS: Malta: Update GCMP detection.

Add GCMP detection for IASim Marvell chip emulation support.

Signed-off-by: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Acked-by: Steven J. Hill <Steven.Hill@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Leonid Yegoshin <Leonid.Yegoshin@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/5529/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>