br-ext: embed opensc for pkcs11-tool

Embed opensc package for pkcs11-tool to play with the PKCS11 TA.

Examples of using pkcs11-tool with PKCS11 TA:

  # Get tokens/slots info
  pkcs11-tool --show-info
  pkcs11-tool --list-token-slots
  pkcs11-tool --list-mechanisms

  # Initialize token and user PIN
  pkcs11-tool --init-token --label test-token --so-pin 1234567890
  pkcs11-tool --label test-token --login --so-pin 1234567890 \
              --init-pin --pin ABCDEFGHIJ

  # Generate a 2048bit RSA key
  pkcs11-tool --token-label test-token --pin ABCDEFGHIJ \
              --keypairgen --key-type RSA:2048 --id 123 --label rsa-test-key

  # List token object
  pkcs11-tool --token-label test-token --list-objects

Co-developed-by: Gábor Székely <szvgabor@gmail.com>
Signed-off-by: Gábor Székely <szvgabor@gmail.com>
Signed-off-by: Etienne Carriere <etienne.carriere@linaro.org>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>