package/mbedtls: make compression support a config option

package/mbedtls: make compression support a config option

Enabling TLS compression may make mbedTLS vulnerable to the
CRIME attack [1]. It should not be enabled unless is is sure CRIME and
similar attacks are not applicable to the particulare situation.

As zlib is probably enabled in most systems, the user might end up with
a vulnerable system without knowing. So, instead of enabling compression
support if the zlib package is available, we make the compression support
a config option. This way, the user has to explicitly enable compression
support and is warned by the help text about the risk.

[1] https://tls.mbed.org/kb/how-to/deflate-compression-in-ssl-tls

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>