snow: Set up the i2s0 pins during boot.

BUG=chrome-os-partner:19420
TEST=Built and booted on snow. Beeped in depthcharge through the i2s0 bus.
BRANCH=None

Change-Id: I6729a139091b40d8fd9ba2aa7a8c4e14216d95c5
Signed-off-by: Gabe Black <gabeblack@google.com>
Reviewed-on: https://gerrit.chromium.org/gerrit/64879
Reviewed-by: Stefan Reinauer <reinauer@google.com>
Commit-Queue: Stefan Reinauer <reinauer@google.com>
Tested-by: Stefan Reinauer <reinauer@google.com>

src/mainboard/google/snow/mainboard.c

@@ -202,6 +202,7 @@ static void gpio_init(void)
 	gpio_direction_output(GPIO_X15, 1);
 
 	/* Set up the I2S busses. */
+	exynos_pinmux_i2s0();
 	exynos_pinmux_i2s1();
 }