km: common: implement field fail-safe u-boot update
This patch provides possibility for field fail-safe u-boot updates.
The implementation can be used on all pg-wcom boards that are booting from
parallel NOR flash.
When used in a board design, provided check_for_uboot_update function will
start new u-boot at defined location if updateduboot envvar is set to yes.
With this implementation it is expected that factory programmed u-boot
will always stay as it is, and optionally new u-boot can be safely
programmed by embedded software when the unit is rolled out on the field.
It is expected check_for_uboot_update to be called early in execution
before relocation (*_f) once SoC is basically initialized and environment
can be read, with this possibilities to not be able to fix a u-boot bug by
a u-boot update are reduced to minimum.
Signed-off-by: Aleksandar Gerasimovski <aleksandar.gerasimovski@hitachienergy.com> Reviewed-by: Priyanka Jain <priyanka.jain@nxp.com>