FM radio McBSP1 special config for Si4721 added back

here is the missing bit of the patch taken from the one in the 3.7-neil-plus
tree. With that, the McBSP1 does work again.

Signed-off-by: Andreas Kemnade <andreas@kemnade.info>
Acked-by: H. Nikolaus Schaller <hns@goldelico.com>