Add PSA inject entropy config option and testing

[ronald-cron-arm]

• [ ] Add PSA_CRYPTO_INJECT_ENTROPY config option and its documentation in the section "PSA cryptography core configuration options" of crypto_config.h. Similar to MBEDTLS_PSA_INJECT_ENTROPY in mbedtls. Disabled by default.
• [ ] Add its translation to MBEDTLS_PSA_INJECT_ENTROPY in config_adjust_mbedtls_from_psa_crypto.h. MBEDTLS_NO_DEFAULT_ENTROPY_SOURCES needs to be defined here as well.
• [ ] Add a test_psa_inject_entropy test component similar to the one in mbedtls.
• [ ] Check that the test component do what it intends to do and give evidence of this in this issue or the associated PR for the benefit of reviewers

Depends on:

• 58 to set up the full config

[gilles-peskine-arm]

We will remove entropy injection in its current form in TF-PSA-Crypto 1.0. This is part of the RNG redesign which will likely not be completed before the 1.0 release, but since it's an API break we will definitely remove the option before 1.0.

Therefore we shouldn't spend any time making it work in TF-PSA-Crypto.