Fix doxygen warnings
Fix doxygen warnings

* Broken link #PSA_ALG_SHA_256
* Duplicate group name "generators"
* Missing documentation in psa_generate_key_extra_rsa due to bad magic
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ARMmbed/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls