Some i.MXes use __NA_ or 0 to avoid setting mux_mode, but the following patch
only take i.MX6/7 into consideration.

"c3c8a574 imx-common: fix iomux settings"

Use is_soc_type(MXC_CPU_MX7) to avoid breaking other i.MXes when
setting mux_mode.

In this patch, switch to use "asm/imx-common/sys_proto.h" to avoid
build break for "is_soc_type" for vf610 and mx25.
Signed-off-by: NPeng Fan <Peng.Fan@freescale.com>
Cc: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: NStefano Babic <sbabic@denx.de>
Reviewed-by: NBenoît Thébaudeau <benoit.thebaudeau.dev@gmail.com>