[nrf noup] zephyr: disabled EXT_API_ATLEAST_OPTIONAL

Disabled at last optional EXT_API when external-crypto is enabled.

Signed-off-by: Andrzej Puzdrowski <andrzej.puzdrowski@nordicsemi.no>
(cherry picked from commit 1d02303)

Author: nvlsianpu

boot/zephyr/external_crypto.conf

@@ -18,4 +18,3 @@ CONFIG_SB_CRYPTO_CLIENT_ECDSA_SECP256R1=y
 CONFIG_SB_CRYPTO_CLIENT_SHA256=y
 CONFIG_BL_SHA256_EXT_API_REQUIRED=y
 CONFIG_BL_SECP256R1_EXT_API_REQUIRED=y
-CONFIG_EXT_API_PROVIDE_EXT_API_ATLEAST_OPTIONAL=y