Update signiture algorithm handling
Update signiture algorithm handling

Rename local variables and to simplify things use static_assert to
determine if the default signiture algorithms are not fit into the
SSL handshake structure.

Signed-off-by: Gabor Mezei <73922791ae56b2f06debbf18b6e0a93a4bcd29f9@arm.com>

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