Revert "arm: imx: mx7: Move CONFIG_OPTEE_TZDRAM_SIZE from lib/optee"

This reverts commit c5b68ef8.

CONFIG_OPTEE_TZDRAM_SIZE is used by imx6-based SoCs as well. Move the
option back.

Signed-off-by: Ricardo Salveti <ricardo@foundries.io>
Signed-off-by: Oleksandr Suvorov <oleksandr.suvorov@foundries.io>