Bluetooth: Host: use P256-M in ECC emulation

When BT_SEND_ECC_EMULATION and the platform uses Mbed TLS as PSA
Crypto provider, we select the Cortex-M software optimized
implementation of the secp256r1 curve algorithms. This is much
faster than the standard support provided by Mbed TLS and it
also reduces ROM footprint.

Signed-off-by: Valerio Setti <[email protected]>

Author: valeriosetti

subsys/bluetooth/host/Kconfig

@@ -1006,6 +1006,7 @@ config BT_SEND_ECC_EMULATION
 	select PSA_WANT_ALG_ECDH
 	select PSA_WANT_KEY_TYPE_ECC_KEY_PAIR_GENERATE
 	select PSA_WANT_ECC_SECP_R1_256
+	select MBEDTLS_PSA_P256M_DRIVER_ENABLED if MBEDTLS_PSA_CRYPTO_C
 	select BT_LONG_WQ
 	depends on BT_ECC && (BT_HCI_RAW || BT_HCI_HOST)
 	default y if BT_CTLR && !BT_CTLR_ECDH