ssb: pick PCMCIA host code support from b43 driver

ssb bus can be found on various "host" devices like PCI/PCMCIA/SDIO.
Every ssb bus contains cores AKA devices.
The main idea is to have ssb driver scan/initialize bus and register
ready-to-use cores. This way ssb drivers can operate on a single core
mostly ignoring underlaying details.

For some reason PCMCIA support was split between ssb and b43. We got
PCMCIA host device probing in b43, then bus scanning in ssb and then
wireless core probing back in b43. The truth is it's very unlikely we
will ever see PCMCIA ssb device with no 802.11 core but I still don't
see any advantage of the current architecture.

With proposed change we get the same functionality with a simpler
architecture, less Kconfig symbols, one killed EXPORT and hopefully
cleaner b43. Since b43 supports both: ssb & bcma I prefer to keep ssb
specific code in ssb driver.

This mostly moves code from b43's pcmcia.c to bridge_pcmcia_80211.c. We
already use similar solution with b43_pci_bridge.c. I didn't use "b43"
in name of this new file as in theory any driver can operate on wireless
core.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>