uboot-phytec

imx: define ARCH_MXC for i.MX8/8M/7ULP

Without this definition, fsl_esdhc will access reserved registers
on i.MX chips, so define ARCH_MXC to fix it.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>