bcma: add stub for bcma_bus_suspend()

.. and connect it up with the pci host bcma driver.

Now, the next step is to connect those bcma bus-level suspend/resume
functions to the actual bcma device suspend resume functions.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>