libssh2: Make crypto backends selectable

This adds a choice to menuselect so people can select if they would like
to compile libssh2 against mbedtls (default) or openssl.

Signed-off-by: Sebastian Kemper <sebastian_ml@gmx.net>

libs/libssh2/Config.in

@@ -0,0 +1,15 @@
+if PACKAGE_libssh2
+
+choice
+	prompt "Choose crypto backend"
+	default LIBSSH2_MBEDTLS
+
+	config LIBSSH2_MBEDTLS
+	bool "mbedtls"
+
+	config LIBSSH2_OPENSSL
+	bool "openssl"
+
+endchoice
+
+endif