imx: move imx8 sci header file to include/firmware/imx

Move imx8 sci header file to include/firmware/imx, then we could
use build macro to reuse some i.MX8 drivers for i.MX9, such as
drivers/cpu/imx8_cpu.c.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Stefano Babic <sbabic@denx.de>
41 files changed