Add fall back option, to boot from NOR/QSPI/SD for LS1043, LS1046,
LS1021 in case of distro boot failure.

For LS1046, add kernel validation in case of secure boot in sd_bootcmd
and qspi_bootcmd. For LS1043 and LS1021, add kernel validation in case
of secure boot in sd_bootcmd, qspi_bootcmdand  nor_bootcmd.
Signed-off-by: NVinitha Pillai <vinitha.pillai@nxp.com>
Reviewed-by: NYork Sun <york.sun@nxp.com>