stm32mp1: dynamically detect op-tee presence

Activate OP-TEE driver for trusted and optee defconfig.

This driver allows detection of TEE presence for boot from flash;
CONFIG_STM32MP1_OPTEE is also removed.

Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@st.com>