pkcs11-tests: Remove access to mbedtls "private" fields patch

This patch can be removed and substituted by using
target_compile_definitions() CMake function to
define `MBEDTLS_ALLOW_PRIVATE_ACCESS` for pkcs11
integration tests source files (core_pkcs11_test.c and
dev_mode_key_provisioning.c) as they both need to define
this macro as part of their source files to be able to
access mbedtls private fields.

Signed-off-by: Ahmed Ismail <Ahmed.Ismail@arm.com>