Fix errors in the definition of MBEDTLS_PK_SIGNATURE_MAX_SIZE
Fix errors in the definition of MBEDTLS_PK_SIGNATURE_MAX_SIZE

The initial value for the max calculation needs to be 0. The fallback
needs to come last. With the old code, the value was never smaller
than the fallback.

For RSA_ALT, use MPI_MAX_SIZE. Only use this if RSA_ALT is enabled.

For PSA, check PSA_ASYMMETRIC_SIGNATURE_MAX_SIZE, and separately check
the special case of ECDSA where PSA and mbedtls have different
representations for the signature.

ARMmbed/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,ARMmbed/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,ARMmbed/mbedtls,Mbed-TLS/mbedtls,NXPmicro/mbedtls,Mbed-TLS/mbedtls