imx: imx8qm/qxp: Recover SPL data section for partition reboot

When doing partition reboot, the boot image won't be reloaded by ROM,
it is just CPU reset to boot entry. The SW has to keep the boot image
inside the RAM unchanged. It includes both the TEXT section and DATA
section.

For SPL, the problem is DATA section will be updated at runtime, so in
next partition reboot the data is not same as the initial value from
cold boot. If any code depends on the initial value, then it will have
problem.

This patch introduces a mechanism to recover the data section
for partition reboot. It adds a new section in image for saving
data section. When from cold boot, the data section will be saved
to that new section at SPL early phase. When from partition reboot,
the data section will be restored from the new section.

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