Remote controller support should be optional on all drivers.

Make it optional at Siano's driver.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

siano is, in fact, 2 drivers: one for MMC and one for USB, plus
a common bus-independent code. Break it accordingly.
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>