tee: optee: bind rng optee driver

In U-Boot, the discovery of TA based on its UUID on the TEE bus is
not supported.

This patch only binds the driver associated to the new supported
OP-TEE TA = TA_HWRNG when this driver is enable.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>