package/optee-examples: new package

package/optee-examples: new package

This package generates embedded Linux based OS userland client
applications and OP-TEE OS trusted applications all embedded in the
file system. These applications shows how to use the APIs OP-TEE OS is
based on, both in the non secure and secure worlds.

Package is added next to the OP-TEE client package in the BR package
configuration.

This change references in Buildroot the today's latest OP-TEE revision
release tagged 3.4.0 with an added patch to fix an issue reported by
recent GCC toolchains.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
[Thomas:
 - drop version selection
 - propagate !BR2_STATIC_LIBS dependency of optee-client
 - make sure BR2_TARGET_OPTEE_OS_SDK is selected
 - use a patch generated by git format-patch
 - simplify the construct to build the examples]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>