Building SPL fails with MBEDTLS enabled.
Currently we don't need it there.
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Acked-by: Jerome Forissier <jerome.forissier@linaro.org>
(cherry picked from commit c7401fc1d9)
[Conflict resolved: kept PHASE_ macro syntax instead of XPL_, kept mbedtls_options.h include instead of inline MBEDTLS_ALLOW_PRIVATE_ACCESS, sha256_csum_wd already exists in sha256_common.c]