ASoC: sun4i-i2s: Update global enable with bitmask

The default value of the config register is different on newer
SoCs and therefore enabling/disabling with a register write
will clear bits used to set the direction of the clock and frame
pins.

Signed-off-by: Marcus Cooper <codekipper@gmail.com>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Mark Brown <broonie@kernel.org>