mbedtls module: Fix for other POSIX arch boards

Instead of detecting that we are in a native/POSIX arch based
board by checking for each board specifically,
let checks for the architecture.
In that way other boards (like the upcoming nrf53_bsim ones)
will also work.

Signed-off-by: Alberto Escolar Piedras <alberto.escolar.piedras@nordicsemi.no>