ASoC: arizona: Add gating for clock when used for direct MCLK

Whilst ultimately we would like to move all the clocking over to the
clock framework, as an intermediate step to get people going for now
gating the source clocks for SYSCLK/ASYNCCLK when they are configured
to come directly from an MCLK pin.

Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Tested-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mark Brown <broonie@kernel.org>