imx: Update FSL_MFGPROT config for iMX8M

Update the Kconfig and Makefile to allow build for iMX8M and
restrict the build only in u-boot.

Signed-off-by: Ye Li <ye.li@nxp.com>
Reviewed-by: Gaurav Jain <gaurav.jain@nxp.com>
2 files changed