i2400m: firmware loading and bootrom initialization

Implements the firmware loader (using the bus-specific driver's
backends for the actual upload). The most critical thing in here is
the piece that puts the device in boot-mode from any other
(undetermined) state, otherwise, it is just pushing the bytes from the
firmware file to the device.
Signed-off-by: NInaky Perez-Gonzalez <inaky@linux.intel.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>