MIPS: ralink: add a symbol for INTC

Some of the newer SoCs use the GIC. This patch splits the INTC out into its
own symbol, allowing us to add the gic code in the following patch.

Signed-off-by: John Crispin <blogic@openwrt.org>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/11989/


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