Using embedTLS for secure boot in nrf9160

I want to use Mbedtls for secure boot so I got to know that I should define CONFIG_BOOT_MBEDTLS
1.but when use that I am getting error as,

error: BOOT_USE_MBEDTLS (defined at
1> C:/Users/Anitha.S/ncs/CL5G_R200/bootloader/mcuboot/boot/zephyr/Kconfig:48) is assigned in a
1> configuration file, but is not directly user-configurable (has no prompt). It gets its value
1> indirectly from other symbols. 
Please suggest which configuration I need to do, please.

my project conf

# TFM configuration
CONFIG_BUILD_WITH_TFM=n
CONFIG_TFM_MCUBOOT_IMAGE_NUMBER=1
# Currently IPC isn't supported with NCS mcuboot
CONFIG_TFM_IPC=y
# MbedTLS and security
CONFIG_NET_SOCKETS_SOCKOPT_TLS=y
CONFIG_NET_SOCKETS_OFFLOAD_TLS=n
CONFIG_MBEDTLS_ENABLE_HEAP=y
CONFIG_MBEDTLS_SSL_MAX_CONTENT_LEN=4096
CONFIG_MBEDTLS_HEAP_SIZE=32768
CONFIG_MBEDTLS_TLS_LIBRARY=y
CONFIG_MBEDTLS_X509_LIBRARY=y
CONFIG_MBEDTLS_PSA_CRYPTO_C=y
CONFIG_MBEDTLS_PKCS1_V15=y
CONFIG_MBEDTLS_RSA_C=y
CONFIG_MBEDTLS_SHA1_C=y
CONFIG_MBEDTLS_LIBRARY_NRF_SECURITY=y
CONFIG_NRF_SECURITY_ADVANCED=y
CONFIG_NORDIC_SECURITY_BACKEND=y

and mcuboot.conf is
CONFIG_BOOT_SIGNATURE_TYPE_ECDSA_P256=y
#CONFIG_BOOT_USE_MBEDTLS=y
CONFIG_SECURE_BOOT_CRYPTO=y
CONFIG_BOOT_ENCRYPT_EC256=y

2.when I use CONFIG_BOOT_ENCRYPT_EC256=y

I get following error please tell me what is the dependency configuration i need to do for this to work.

"One crypto backend must be defined: either MBED_TLS or TINYCRYPT"
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