MIPS: Malta: GIC IPIs may be used without MT

It's perfectly valid to use SMP on a non-MT CPU and use the GIC for
IPIs. Set them up conditional upon CONFIG_MIPS_GIC_IPI rather than
CONFIG_MIPS_MT_SMP.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Cc: Paul Burton <paul.burton@imgtec.com>
Patchwork: https://patchwork.linux-mips.org/patch/6654/


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