modules: tf-m: make CONFIG_BUILD_WITH_TFM imply CONFIG_MBEDTLS

This fixes NS compilation on certain app/board combinations
where TF-M is used but CONFIG_MBEDTLS was not set to y.

With the update to MbedTLS 3.6.0, the compilation failed in
(at least) interface/src/tfm_crypto_api.c when trying to
include MbedTLS configuration file because the MbedTLS Kconfigs
were not defined due to CONFIG_MBEDTLS being n (and the default
MbedTLS configuration file not being found).

TF-M's dependency on MbedTLS is pretty much a given.
This change ensures that the configuration for MbedTLS
is properly defined at all times when TF-M is in use.

Signed-off-by: Tomi Fontanilles <tomi.fontanilles@nordicsemi.no>