pcmcia: add new CIS access helpers

As a replacement to pcmcia_get_{first,next}_tuple() and
pcmcia_get_tuple_data(), three new -- and easier to use --
functions are added:

- pcmcia_get_tuple() to get the very first CIS entry of one
  type.

- pcmcia_loop_tuple() to loop over all CIS entries of one type.

- pcmcia_get_mac_from_cis() to read out the hardware MAC address
  from CISTPL_FUNCE.

Only a handful of drivers need these functions anyway, as most
CIS access is already handled by pcmcia_loop_config(), which
now shares the same backed (pccard_loop_tuple()) with
pcmcia_loop_tuple().

A pcmcia_get_mac_from_cis() bug noted by Komuro
<komurojun-mbn@nifty.com> has been fixed in this revision.

Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>