mfd: arizona: Add gating of external MCLKn clocks

This patch adds requesting of the clocks supplied on MCLK1, MCLK2 pins,
gating of the 32k clock is added to the arizona_clk32k_enable(),
arizona_clk32k_disable() helpers.

It's a temporary change until the CODEC's clock controller gets exposed
through the clk API and is helpful for board configurations where the
MCLK clocks are not provided by always on oscillators.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.wolfsonmicro.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>