pcmcia/yenta: guide users in case of problems with O2-bridges

Some cards need the speedups on, some need them off. As we can't detect
this reliably, at least give the users a hint how to tweak the system.

Reported-by: David Bluecame <david.bluecame@gmail.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>