tests: tls_configurations: adjust Kconfig in overlay-ec

CONFIG_PSA_WANT_KEY_TYPE_ECC_KEY_PAIR_BASIC is promptless so it cannot
be selected. Moreover it's also automatically enabled by
CONFIG_PSA_WANT_KEY_TYPE_ECC_KEY_PAIR_GENERATE in the same overlay file
so there would be no need to explicitly enable it.

As for the IMPORT, EXPORT, DERIVE they are needed for the TLS connection
to work properly. Previously it was working because at least IMPORT and
EXPORT are internally enabled by Mbed TLS at build time. So here we
are basically doing the same enablements with Kconfigs in clear.

Signed-off-by: Valerio Setti <vsetti@baylibre.com>