pcmcia: rsrc_nonstatic io memory probe improvements

Add a lot of documentation to the rsrc_nonstatic io memory probe
functions. Also, add a first memory probe call -- just checking
whether request_resource() succeeds -- upon adding of resources.

Tested-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>