soc: imx: select ARM_GIC_V3 for i.MX8M

Select ARM_GIC_V3, then it is able to use gic v3 driver in aarch32
mode linux on aarch64 hardware. For aarch64 mode, it not hurts
to select ARM_GIC_V3.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>