serial: Kconfig: make MXC_UART usable for MX7 and IMX8M

i.MX7 and i.MX8M use mxc uart driver, so let's make the SoC could
use MXC_UART kconfig.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Ye Li <ye.li@nxp.com>
1 file changed