optee: bind the TA drivers on OP-TEE node

In U-Boot driver model the devices can be referenced by
phandle in the U-Boot configuration nodes.

Without a valid node provided during the bind, the driver
associated to OP-TEE TA can't be referenced.

For example to force the sequence number with alias
(.flags = DM_UC_FLAG_SEQ_ALIAS)

 	aliases {
		rng0 = &optee;
 	};

or other configuration:

board-sysinfo {
   compatible = "vendor,sysinfo-board";
   ramdom = <&optee>;
}

With this patch all drivers bound from OP-TEE service
discovery are now associated are associated to OP-TEE
node, allowing to identify by phandle the driver
provided by the TA for one UCLASS without modifying
device tree.

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