package/optee-client: new package

package/optee-client: new package

OP-TEE client API library and supplicant daemon from the
OP-TEE project are packaged in package/optee-client. An init script
launches the tee-supplicant deamon. Package is added to the
Security menu of BR configuration.

This change references in Buildroot the today's latest OP-TEE
revision release tagged 3.4.0.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
[Thomas:
 - remove version selection
 - add dependency on !BR2_STATIC_LIBS, as it unconditionally builds a
   shared library]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>