Parsing a key and importing it into PSA may result in a policy that
specifies an algorithm that is not included in the build. This happens if
the key type is supported, but not the algorithm, e.g. in a build with
MBEDTLS_ECP_C but not MBEDTLS_ECDSA_C.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>