wl1271: Add wl1271_load_firmware() and export some functions

For the SDIO testing module we need to load the firmware but not
boot it. wl1271_load_firmware() is meant to do just the firmware loading part.

We also export some functions so they are usable in the testing module.

Signed-off-by: Roger Quadros <roger.quadros@nokia.com>
Signed-off-by: Luciano Coelho <luciano.coelho@nokia.com>