arm: socfpga: Add clock for smp_twd timer

Assign a clock for the twd-timer.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Cc: Pawel Moll <pawel.moll@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Ian Campbell <ian.campbell@citrix.com>
CC: linux-arm-kernel@lists.infradead.org