Fix Atmel soc audio boards Kconfig dependency

Add Kconfig dependency on AT91_PROGRAMMABLE_CLOCKS for the Atmel SoC
audio SAM9G20-EK and PlayPaq boards. Fixes link errors on missing
clk_set_parent and clk_set_rate when building without
AT91_PROGRAMMABLE_CLOCKS.

Signed-off-by: Ryan Mallon <ryan@bluewatersys.com>
Acked-by: Geoffrey Wossum <gwossum@acm.org>
Acked-by: Liam Girdwood <lrg@slimlogic.co.uk>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>