package/optee-test: add deps on openssl when enabled

package/optee-test: add deps on openssl when enabled

Add a dependency on openssl upon BR2_PACKAGE_LIBOPENSSL=y to
enable some for OP-TEE embedded tests.

Building with libressl makes the optee-test test tool fail on a
certificate test; so we explicitly depend on libopenssl.

Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
[yann.morin.1998@free.fr:
  - match the depenency to libopenssl, since that's is what is used in
    the condition (BR2_PACKAGE_LIBOPENSSL)
  - add a blurb to explain why libopenssl is used, not the virutal
    openssl
]
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>