[media] siano: break it into common, mmc and usb

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: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/common/Makefile b/drivers/media/common/Makefile
index f3afd83..b8e2e3a 100644
--- a/drivers/media/common/Makefile
+++ b/drivers/media/common/Makefile
@@ -1 +1 @@
-obj-y += b2c2/ saa7146/
+obj-y += b2c2/ saa7146/ siano/