imx8m: Restrict usable memory based on rom_pointer[0]

When TEE is loaded, we need to restrict the memory usage based
on rom_pointer[0]

Signed-off-by: Ying-Chun Liu (PaulLiu) <paulliu@debian.org>
Cc: Fabio Estevam <festevam@denx.de>
Cc: Frieder Schrempf <frieder.schrempf@kontron.de>
Cc: uboot-imx <uboot-imx@nxp.com>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>